Prepare the cake pan. Preheat an oven to 325F. Line a 9 inch cake pan or springform pan with parchment, then spray generously with baking spray or butter.
Cream the butter and sugar. Place ½ cup softened butter, 1 ⅓ cup granulated sugar, 2 tsp vanilla extract, and 1 tsp almond extract into the bowl of a stand mixer fitted with paddle attachment. Begin on medium speed, then increase to medium-high and beat until very smooth, 5 minutes.
Incorporate egg yolks. Add the egg yolks, one at a time, scraping down the sides between additions.
Whip the ricotta. Add the ricotta cheese and lemon zest, then continue beating on medium speed until very smooth, an additional 5 minutes. Pour in the almond flour then add a pinch fo Kosher salt. Mix until just combined. Transfer the mixture to a large mixing bowl, then clean and wipe out the bowl of the stand mixer very well.
Beat the egg whites. Replace the paddle with the whisk attachment, then beat the egg whites on medium-high speed until stiff peaks form. Gently fold half of the egg whites into the cake batter until just mixed in. Repeat with remaining egg whites.
Bake the cake. Pour the cake batter into the greased cake pan. Sprinkle the sliced almonds evenly over the top of the cake, then bake for 50-55 minutes, or until the top and sides of the cake are firm and a cake tester inserted into the center of the cake comes out clean.
Cool, then slice. Allow the cake to cool for 10-15 minutes, then carefully remove the outer ring of the pan. Dust with confectioner’s sugar, then slice and serve warm or at room temperature.