Marble muffins

Preparation

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  Whisk eggs with sugar. Add yogurt and combine. Add flour and baking powder and mix well. Finally : add the melted butter and mix again.
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  Divide the batter in two batters : in the first batter add the cocoa powder. Mix well.
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  In the second batter add the vanilla extract and mix well.
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  Pour randomly the batters in the muffin tins with tablespoons.
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  Make some swirls with a wooden stick.
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  Bake for 15 minutes at 350°F (180°C).
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  Remove from oven and leave to cool down. You can add some chocolate spread inside and on top of your muffins.