Preheat oven to 350. Spray a 9-inch springform pan with cooking spray. Put the ¼ cup almond flour and 1 teaspoon sweetener in the pan and tap and tilt the pan until it covers the bottom.
Next, make the cheesecake filling. With an electric mixer or food processor mix the cream cheese until fluffy. Add sweetener, lemon zest, and sour cream. Mix until smooth. Add eggs one at a time, mixing after each addition. Pour into prepared pan. Bake the cheesecake for 25 min.
Meanwhile, make the cake batter. In the same bowl or food processor cream the butter and sweetener until light and fluffy. Add the sour cream and lemon zest and beat until combined. Add the eggs one at a time mixing after each. Stir in the flours, baking powder, and salt until thoroughly combined.
After the cheesecake has baked for 25 minutes drop small dollops of the cake batter all over it. Do not pour it on, it will sink. The best way it to just drop small spoonfuls on top until it is covered. Bake for an additional 35 minutes or until puffed up and golden. Cool completely.
To make the lemon curd melt the butter and sweetener in a small saucepan over medium-low heat. Cook until slightly thickened. Turn off the heat and cool for 5 minutes. Whisk in the egg yolks one at a time. Turn the heat back on medium-low and cook until thick. Add the lemon juice and whisk until smooth. Strain through a fine mesh strainer in case there are any bits of scrambled yolk. Cool to room temperature and then use to top the lemon cake.
Chill in the fridge for at least 4 hours before serving.