Mix heavy cream, buttermilk, and 2 tablespoons sugar together in a bowl. Let stand at room temperature until slightly thickened, 6 to 8 hours. Cover and refrigerate for at least 24 hours before using.
Sift flour, baking powder, and salt together in a bowl.
Whisk ricotta cheese, egg yolks, milk, sugar, and lemon zest together in a separate bowl. Whisk in flour mixture until batter is smooth.
Beat egg whites in a glass, metal, or ceramic bowl until stiff peaks form. Fold very gently into the batter.
Heat a lightly oiled griddle over medium heat. Drop 1/2 cup batter onto the griddle and cook until bubbles form and the edges are dry, 3 to 4 minutes. Flip and cook until browned on the other side, 2 to 3 minutes. Repeat with remaining batter.
Beat sweetened creme fraiche until stiff peaks form. Serve with pancakes.
