Preheat oven to 350°F with a rack in the middle of the oven. Line the bottom of an 8-inch round cake pan with parchment paper and grease the pan.
Crumble almond paste into a food processor bowl. Add granulated sugar and pulse until finely ground. Add butter and process until smooth. Add eggs and almond extract and process until combined, scraping the sides and bottom of the bowl occasionally. Add flour, baking powder, and salt, and process until blended.
Pour batter into prepared pan and smooth the top. Tap the pan on the countertop a few times to remove air bubbles. Top the cake batter with sliced almonds and sugar.
Bake for 23-26 minutes, or until a toothpick inserted into the center comes out clean. Cool in the pan on a wire rack for 30 minutes, then remove from the pan and cool completely on the rack. Serve slightly warm or at room temperature.