Whisk together the flour, sugar, cocoa, baking soda and salt in a mixing bowl. Beat the eggs in another bowl with a fork or can use mixer. Stir yogurt or sour cream into the eggs along with buttermilk, oil and vanilla extract.
Combine with dry mixture and stir with spoon until all ingredients are wet. Fold in chocolate chips. Mixture will be thick. Spray a 12 cup donut baking pan with cooking spray.
Fill cups about half full. Bake in preheated 375 degree oven for 8 or 9 minutes until donuts test done in the middle. Allow to cool in pan for 10 minutes, remove and let cool completely before adding frosting.
Makes 1 1/2 dozen small donuts.