First make the sauce:
In a small saucepan combine the blueberries, sugar, lemon juice, and water. Cook over medium-high heat, stirring gently until boiling.
Add the cornstarch/water mixture and without breaking the berries- carefully stir it in. Cook for 2-3 minutes over low heat, stirring until sauce is thick. Fold in lemon zest.
For the pancakes:
In a large bowl, whisk together the egg yolks, ricotta, lemon juice and zest. Sprinkle the baking powder, baking soda, salt, sugar and flour over the ricotta mixture and gently fold in.
In a small bowl, beat the egg whites on high speed until stiff peaks form. Fold 1/3 of the egg whites into the batter and then add the rest, gently folding until smooth and airy.
Spoon a scant 1/4 cup batter for each pancake onto a hot skillet or griddle (either use nonstick or add spray or butter before each batch.) Flip pancakes when tops are covered with bubbles and edges look cooked.
Serve pancakes with butter and blueberry sauce