Halloween Spooky Sweet Potato Tart
This tart is two sweet potato pies wearing a costume, which is perfect for halloween! A black cocoa pastry crust holds a deeply spiced orange sweet potato layer, baked the classic way. A thin line of dark chocolate ganache sits on top of it, then a bright purple sweet potato custard that sets in the fridge so it stays purple. Every slice comes out black, orange, and purple without a single drop of food coloring or refined sugar. It takes a while, but most of that time is the fridge!
Equipment
- 9-inch deep tart pan with removable bottom (about 1 ¾" deep)
- Food processor or pastry cutter
- Rolling Pin
- Parchment paper and pie weights (or dried beans)
- Baking sheet
- Steamer basket and pot
- Medium saucepan
- Whisk
- Blender
- Small heatproof bowl
Ingredients
Black cocoa pastry crust
- 1 ½ cups 190g all-purpose flour, plus more for patching
- ¼ cup 20g black cocoa powder
- ½ tsp fine sea salt
- 10 tbsp 142g cold unsalted butter, cubed
- 5 to 8 tbsp ice water
- 1 egg white left over from the orange layer, lightly beaten
Spiced orange sweet potato layer
- 1 ¼ cups mashed roasted orange sweet potato about 1 lb raw
- ½ cup unsweetened evaporated milk
- ⅓ cup maple syrup
- 1 large egg plus 1 egg yolk save the white for the crust
- 2 tbsp unsalted butter melted
- 1 tsp ground ginger
- ½ tsp ground cinnamon
- ½ tsp freshly grated nutmeg
- ½ tsp ground allspice
- ⅛ tsp ground cloves
- Pinch of black pepper
- ½ tsp fine sea salt
- 1 tsp vanilla extract
Soft ganache layer
- 2 oz coconut-sugar-sweetened dark chocolate finely chopped
- ⅓ cup heavy cream
- Pinch of salt
Purple sweet potato custard
- 1 ¼ cups steamed purple sweet potato mashed (about 1 lb raw)
- ⅔ cup whole milk
- ⅓ cup heavy cream
- ⅓ cup maple syrup
- 1 large egg
- 1 ½ tbsp cornstarch
- ⅛ tsp ground cardamom
- ¼ tsp fine sea salt
- 1 tbsp unsalted butter
- ½ tsp vanilla extract
- 1 to 1 ½ tsp fresh lemon juice
- ½ tsp finely grated lemon zest
Instructions
- Make the dough. Pulse the flour, black cocoa, and salt in a food processor until evenly combined. Add the cold butter and pulse until the biggest pieces are pea-sized. Drizzle in 5 tbsp ice water and pulse just until the dough clumps when pinched, adding more water a tablespoon at a time if it’s dry. Cocoa soaks up water, so it will likely need more than plain pastry. Press into a disk, wrap, and chill at least 1 hour.
- Cook the potatoes while the dough chills. Heat the oven to 400°F. Prick the orange sweet potato and roast it on a baking sheet for 45 to 50 minutes, until completely soft. Meanwhile, peel and cube the purple sweet potato and steam it 15 to 20 minutes, until a fork slides through. Roasting the orange one deepens the flavor. Steaming the purple one protects the color. Mash each separately, measure 1 ¼ cups of each, and let them cool.
- Roll and shape the crust. Roll the dough between two sheets of parchment into a 13-inch round. Peel off the top sheet, flip the dough into the tart pan, and peel off the second sheet. Press the dough into the corners and up the sides without stretching it, patch any tears with scraps, and trim the excess. Prick the bottom with a fork and freeze 30 minutes. Set the oven to 375°F.
- Blind bake. Line the cold crust with parchment and fill it with pie weights. Bake 20 minutes, then remove the parchment and weights and bake 8 to 10 minutes more. You can’t judge doneness by color here, so look for a bottom that looks dry and matte instead of shiny. Brush the hot crust with the beaten egg white and return it to the oven for 2 minutes to seal it, which keeps the bottom from going soggy. Lower the oven to 325°F.
- Make the orange layer. Blend or whisk the orange sweet potato, evaporated milk, maple syrup, egg, yolk, melted butter, all the spices, salt, and vanilla until completely smooth. Pour it into the warm crust and smooth the top.
- Bake. Bake at 325°F for 35 to 45 minutes, until the edges are set and the center has only a slight wobble. Since you can’t see the crust edges browning, cover them with strips of foil about halfway through. Cool on a rack 1 hour, then refrigerate 30 minutes so the surface is cold before the ganache goes on.
- Make the ganache. Heat the cream until steaming, pour it over the chocolate and salt, and let it sit 2 minutes. Stir until smooth, then cool about 10 minutes, until lukewarm but still pourable. Pour it over the chilled orange layer and tilt the pan to spread it edge to edge. Chill 20 minutes, until set.
- Start the purple custard. In a bowl, whisk the maple syrup, egg, cornstarch, cardamom, and salt until smooth. Heat the milk and cream in a saucepan until steaming. Slowly whisk half of the hot milk into the egg mixture, then pour it all back into the pan.
- Cook it until it means it. Whisk constantly over medium heat until the custard thickens and bubbles, then keep whisking a full minute more so it sets properly in the fridge.
- Blend. Add the hot custard, purple sweet potato, butter, and vanilla to the blender and blend until silky, venting the lid. Blend in the lemon zest and 1 tsp lemon juice. Taste it, and add the last ½ tsp of juice if the color looks dull or it tastes flat.
- Cool it slightly, then layer. Let the custard sit 10 to 15 minutes, stirring now and then, until warm but no longer hot. Pour it slowly over the back of a spoon onto the set ganache and smooth the top.
- Chill. Press plastic wrap directly onto the surface and refrigerate at least 4 hours, or overnight, until firm enough to slice.
Notes
Substitutions
Plain pastry crust: Leave out the black cocoa and start with 4 tbsp ice water. You’ll get a golden crust instead, and the ganache still gives you a black stripe.
A store-bought pie dough works, but most rounds are too small for a deep tart pan. Check that yours rolls to 13 inches, or plan on piecing it.
Heavy cream can replace the evaporated milk in the orange layer. It comes out a little richer and a little less classic. Optional add-ins
Spiderweb top: Thin ¼ cup sour cream with 1 tbsp cream and 1 tsp maple. Right after pouring the purple layer, pipe concentric circles on top and drag a toothpick from the center outward. Tips
Check the potato. Stokes Purple (purple skin, purple inside) gives true purple. Okinawan (beige skin) comes out pale lavender. If the label just says “purple,” cut one open before you commit.
The black cocoa dough is a little more fragile than plain pastry. Rolling it between parchment makes it much easier, and patches won’t show once it’s baked.
Keep everything cold when making the dough. If it gets soft or sticky while you roll it, put it back in the fridge for 10 minutes.
For the cleanest stripes, slice cold with a hot, dry knife and wipe it between every cut.
The steps can easily be split across 2 days for ease. Make the dough, crust, and orange layer one day, then do the ganache and purple layer the next. Storage
Keep covered in the fridge for up to 3 days. Don’t freeze it: the cornstarch custard weeps when thawed.
Plain pastry crust: Leave out the black cocoa and start with 4 tbsp ice water. You’ll get a golden crust instead, and the ganache still gives you a black stripe.
A store-bought pie dough works, but most rounds are too small for a deep tart pan. Check that yours rolls to 13 inches, or plan on piecing it.
Heavy cream can replace the evaporated milk in the orange layer. It comes out a little richer and a little less classic. Optional add-ins
Spiderweb top: Thin ¼ cup sour cream with 1 tbsp cream and 1 tsp maple. Right after pouring the purple layer, pipe concentric circles on top and drag a toothpick from the center outward. Tips
Check the potato. Stokes Purple (purple skin, purple inside) gives true purple. Okinawan (beige skin) comes out pale lavender. If the label just says “purple,” cut one open before you commit.
The black cocoa dough is a little more fragile than plain pastry. Rolling it between parchment makes it much easier, and patches won’t show once it’s baked.
Keep everything cold when making the dough. If it gets soft or sticky while you roll it, put it back in the fridge for 10 minutes.
For the cleanest stripes, slice cold with a hot, dry knife and wipe it between every cut.
The steps can easily be split across 2 days for ease. Make the dough, crust, and orange layer one day, then do the ganache and purple layer the next. Storage
Keep covered in the fridge for up to 3 days. Don’t freeze it: the cornstarch custard weeps when thawed.