Place a rack in the center of your oven and preheat the oven to 350 degrees F. Lightly grease an 8-inch round pan with butter or coconut oil, coating the bottom and up the sides. Line the bottom with parchment paper, then coat again. Sprinkle 2 tablespoons sugar into the bottom of the pan.
In the bowl of a standing mixer fitted with the whisk attachment or a large mixing bowl, place the egg whites, 1/4 cup sugar, vanilla extract, almond extract, and cream of tartar. With an electric mixer (or stand mixer) beat the egg whites on low speed until they become foamy, then increase the speed to high and continue to beat until they form soft peaks. Reduce the mixer speed to low, then gradually add the remaining 1/4 cup sugar. Continue mixing on low until combined. Set aside.
In a separate bowl, stir together the almond flour, baking powder, and salt. Add the egg yolks, then stir to combine. The dough will be very thick, dry, and crumbly.
Working 1/2 cup at a time, gently fold in the egg whites, completely incorporating them between each addition. The batter will be very thick at first but will lighten as you progress. Fold in the lemon zest.
Scrape the cake batter into the prepared pan and smooth the top. Bake on the center rack for 28 to 32 minutes, until it is light golden brown and a toothpick inserted into the center comes out clean. Remove from the oven, place on a wire rack, and let cool in the pan for 5 minutes. Run a sharp knife along the edge of the cake to loosen it, then gently turn the cake out onto a serving plate and let cool completely. Serve with berries, almonds, and whipped cream, as desired.
Notes
TO STORE: Undecorated cake may be stored at room temperature, in an airtight container, for up to 3 days. Once decorated with fruit and whipped cream, the cake should be stored in the refrigerator.
TO FREEZE: Let it cool completely, then tightly wrap it in plastic and place in the freezer for up to 2 months. Let it thaw in the refrigerator overnight before serving.