Step 1: Preheat your oven to 350°F (175°C).
Step 2: Line a 9-inch round cake pan with parchment paper and lightly grease the sides.
Step 3: Whisk the egg yolks with 1 cup of sugar until pale and creamy. Add vanilla and almond extracts.
Step 4: Sift together almond flour, baking powder, and kosher salt in another bowl.
Step 5: Gradually fold dry ingredients into the egg yolk mixture until just combined.
Step 6: Beat the egg whites with cream of tartar until soft peaks form, gradually adding remaining sugar.
Step 7: Fold the whipped egg whites into the batter in three additions.
Step 8: Fold in the lemon zest.
Step 9: Pour the batter into the prepared pan and bake for 25-30 minutes until a toothpick comes out clean.
Step 10: Cool the cake for 10 minutes in the pan before transferring to a wire rack.