Preheat the oven to 350º F.
Whisk flour and sugar in a medium bowl.
Whisk egg yolks and melted coconut oil together in a small bowl.
Whisk in the milk, yogurt, lemon juice and zest into the egg yolk mixture.
Pour the lemon mixture into the flour and sugar and whisk to blend.
Add the egg whites to a mixing bowl. Mix on high speed until they form stiff white peaks.
Gently fold the egg whites into the lemon cake batter.
Lightly grease mini bundt pans, or a springform pan.
Put the pans into a larger pan with ½ inch of water. (*If you use a springform pan, wrap the bottom in foil so no water gets in the bottom.)
Bake 25 minutes for the small bundt pans and around 40 minutes for the springform pan. (I didn't make this in a large pan so you will need to keep an eye on it if you use this size pan.)