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In a large bowl, mix flour, granulated sugar, brown sugar, baking powder, baking soda, espresso powder, and salt together.
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Make a well in the center of the dry ingredients (push the dry ingredients up around the sides so there’s a hole or ‘well’ in the center—this helps disperse the wet ingredients better).
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Pour in the buttermilk, oil, brewed coffee, and eggs.
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Gently mix the batter until the wet ingredients are just mixed in (the batter will still be very dry at this point).
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Add in the sour cream and vanilla extract, and mix until all of the ingredients are just combined.
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Lastly, add in the mini chocolate chips and mix until combined.
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Fill the muffin tins about 2/3 of the way full with the batter. The batter makes about 12-14 muffins.