Baked Chocolate-Coffee Donuts
Ingredients:
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1 teaspoon unsalted butter
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1 cup all-purpose flour
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¼ cup unsweetened cocoa powder
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1 teaspoon baking powder
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½ cup packed brown sugar
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¼ cup buttermilk
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2 tablespoons buttermilk
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¼ cup strong brewed coffee
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1 egg
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1 tablespoon unsalted butter
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½ teaspoon vanilla extract
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¼ cup chocolate chips, or to taste