1 cup almonds (blanched or unblanched), ground to a fine powder in a blender or food processor (be careful not to over-process or you’ll end up with almond butter!)
2 tablespoons butter, melted
2 tablespoons sugar
For the lemon curd filling:
6 egg yolks
½ cup sugar
⅓ cup fresh lemon juice (plan on about 2-3 lemons)
Zest from one lemon
½ cup (1 stick) unsalted butter, cut into pieces
Confectioners' sugar, for serving
Instructions
Make the crust: Mix the ground almonds, melted butter, and sugar together in a small bowl. Pour into an 8-by-8-inch square pan (or 8½-inch round) lined with parchment paper. Use the back of the spoon to spread and press the mixture together to cover the bottom of the pan. Bake at 350°F for 8 to 10 minutes, until just beginning to look golden and dry. Let cool. Turn oven down to 300°F.
Make the filling: In a large heatproof metal or glass bowl, whisk the egg yolks, sugar, lemon juice, and lemon zest together. Place on top of a pot of simmering water and add the butter a few pieces at a time until melted and combined, stirring frequently. Continue to cook over the simmering water for an additional 10 to 12 minutes, stirring frequently, until thick and coating the back of the spoon. Remove from heat and strain into a shallow bowl to remove any curdled egg bits and keep the filling smooth. Allow to cool to room temperature. Spread the lemon curd filling over the crust and bake at 300°F for 18 to 20 minutes, until the filling is set. Let cool to room temperature, and refrigerate for at least 2 hours before cutting. Dust with powdered sugar if desired.