How to Make It
Heat oven to 400°F. Combine almonds and hazelnuts in the bowl of a food processor and process until very finely ground, about 1 minute. Spray the bottom and sides of a rimmed baking sheet with cooking spray.
Combine butter, sugar, and lemon zest in large bowl and, using an electric mixer, beat on medium high until pale and fluffy, about 3 minutes. Beat in egg yolks and vanilla.
Combine ground nuts, flour, baking powder, salt, cinnamon, nutmeg, and cloves in a large bowl. Reduce mixer speed to low and slowly add flour mixture until dough holds together when squeezed. Set aside 1½ cups.
Transfer remaining dough to prepared sheet tray, pressing down with fingertips to create an even layer. Use a greased flat-bottomed measuring cup to press the dough evenly into the bottom and up the sides of the pan. Prick all over with fork. Chill 15 minutes. Bake until just beginning to brown around the edges, 10 to 12 minutes. Let cool completely, about 20 minutes. Reduce oven to 350°F.
Press the remaining dough into a thin layer on a parchment lined baking sheet (don't worry about getting this perfect—this will be for your cut-outs). Place in the refrigerator until firm.
Spread jam over cooled crust. Cut out heart shapes from reserved dough in various sizes and carefully arrange over jam. Brush cut-outs with heavy cream and sprinkle with turbinado sugar. Bake until jam is bubbling and crust is golden brown, 30 to 35 minutes. Let cool, then cut into 2 inch squares.