If making your buttermilk, add the lemon juice to the milk and let sit for 15 minutes (this is your buttermilk substitute).
Preheat oven to 425. Spray Donut pan with non-stick spray
Combine dry donut ingredients in large bowl.
Add buttermilk (or the milk with lemon juice or vinegar), eggs and butter.
Stir just until well mixed.
Fill each ring of the donut pan about 2/3 but make sure it doesn't top center hole.
Bake about 8 minutes, until the tops spring back when lightly pressed.
Leave donut in pan for about 5 minutes.
Remove from pan and set on cooling rack.