Preheat oven to 375 degrees F.
Grease an 8-inch springform pan with the tablespoon of butter.
Line bottom of pan with parchment paper.
In a bowl, combine the ground almonds with the flour.
Using an electric mixer, beat 6 ounces of butter with sugar until light and fluffy.
Add the lemon juice and mix.
Add the egg yolks. Continue beating until well combined.
Add the ricotta, lemon zest, and lemon juice. Beat until combined.
Fold in the almond-flour mixture. Set aside.
In a clean bowl, beat the egg whites until stiff peaks form.
Gently fold the whites into the cake mixture.
Pour into the prepared pan.
Bake 45 minutes until lightly browned and still slightly soft in the center.
Remove from oven and allow to cool in the pan.
Dust top with confectioners' sugar.
Serve warm or at room temperature.