In a large bowl, whisk together the flour, sugar, baking powder, and salt.

In a separate bowl, whisk the egg yolks, buttermilk, ricotta cheese, lemon zest, vanilla extract, and melted butter until smooth.

Pour the wet ingredients into the dry ingredients and stir gently until just combined (a few lumps are okay).

In a clean bowl, beat the egg whites with an electric mixer until stiff peaks form, then gently fold them into the batter to keep it airy.

Heat an æbleskiver pan over medium heat and brush each well with a little melted butter or vegetable oil.

Fill each well about three-quarters full with batter and cook for 2-3 minutes until the bottom is golden and a crust has formed.

Using a skewer or knitting needle, rotate the balls 90 degrees; if desired, add a tiny bit more batter to the center before flipping completely to ensure a round shape.

Continue cooking and turning frequently until the balls are evenly golden brown and cooked through (insert a skewer to test).

Transfer to a warm plate and serve immediately with a dusting of powdered sugar or warm berry jam.