Instructions

1. Combine the flour, cocoa powder, sugar, and salt in the bowl of a food processor, and pulse briefly until everything is well-blended. Add the cold cubed butter and pulse until it is in small pea-sized pieces. Add the egg yolk and pulse in 5-second bursts until the dough starts clumping together.
2. Turn it out of the food processor and knead it lightly several times to incorporate any extra flour and cocoa powder. At this point, the dough can be wrapped and refrigerated for several days. If you’re ready to use it now, spray five 3.5-inch removable bottom tart pans with nonstick cooking spray. Press the dough into the bottom and sides of the pans in a thin, even layer.
3. Freeze the shells for 30 minutes, and while they’re in the freezer, preheat the oven to 375 degrees F. Spray the tops of the tart dough with nonstick spray, then press a sheet of foil into the shells and fill the foil with dry beans, rice, or pie weights. Bake the shells for 10-12 minutes, then carefully remove the foil and weights. Bake for an additional 6-8 minutes to fully bake the shells, until puffed, dry, and fragrant. Let the shells cool completely before filling them.

To Make the Tart Filling:

1. Sift the matcha powder into a small bowl. Add 3 tbsp of cream to the matcha and whisk together until it forms a smooth, thick paste without lumps.
2. Place the chopped white chocolate in a medium bowl and microwave it in 30-second increments, stirring after every 30 seconds, until the white chocolate is melted and smooth. Heat the remaining 3 tbsp cream and 1 tbsp corn syrup in a small saucepan or in the microwave, and when hot, add the hot cream and matcha-cream to the melted chocolate and whisk everything together, until it is smooth and shiny. Divide the matcha white chocolate between the five tart shells, pouring it until it fills the shells halfway. If you have a little extra, set it aside to roll into truffles or eat later.
3. Refrigerate the shells until the matcha layer is set, for about an hour. Prepare the chocolate layer: place the chopped semi-sweet chocolate in a medium bowl. Pour the remaining ½ cup of cream and 1 tbsp corn syrup into a small saucepan and heat until it comes to a simmer, but do not let it boil completely.
4. Pour the hot cream over the chopped chocolate and let it sit for one minute to melt the chocolate. Whisk everything together until the chocolate is smooth and shiny. Pour the chocolate on top of each tart until it comes to the very top, and smooth the top of the tart with a spatula or knife.
5. Refrigerate the tarts again to set the chocolate ganache, for about 1 hour. To decorate them with a “moldy” design, use a clean, food-safe paintbrush with soft bristles. Speckle the top with powdered sugar (see note below) and then dot matcha powder on top of it. If you’re not going for a moldy look, you can brush or sprinkle matcha powder on top or cover the tarts with a doily and sift matcha on top for a beautiful lacy design. The powder will slowly be absorbed into the tart, so it’s best to decorate them shortly before serving. For the best taste and texture, allow these tarts to sit at room temperature for about 20 minutes before serving.