The best chocolate muffins

I spent some time recently to try different chocolate muffin recipes. Main requirements to the chocolate muffin - it should be soft, it should have a lot of butter as an ingredient, I want to feel the chocolate with all my senses. This is the first recipe which meets the criteria - that's why I call these muffins the best chocolate muffins. Yes, I know, tastes differ, but believe me, it is a good and easy recipe. Two little tips: Take care not to overmix the batter; use a flexible spatula to gently fold ingredients together. Take care also not to overbake the muffins - they should remain soft in the middle. 

Ingredients:

• 1 cup flour
• 1/2 cup yogurt
• 1/2 cup melted butter (120 g)
• 1 egg
• 1/2 cup sugar
• 1 Tbsp vanilla sugar
• 3 Tbsp cocoa powder
• 1 teaspoon baking powder
• 100 g dark chocolate
• 8 halves of walnuts

Preparation:

Preheat oven to 180°C (350°F).

Sieve flour, cocoa and baking powder. Melt butter. Chop chocolate into small pieces.

Beat egg, sugar and vanilla sugar until white. Add yogurt and melted butter. Mix well with a spatula and add the flour mixture. Mix again, add the chopped chocolate. Grease a nine-cup muffin tin and line with cupcake papers. Fill muffin tins three-quarters full - they will puff in the oven. Put a half of walnut on top of each muffin and bake for 20 minutes. 
Let muffins cool in the pan for 10 minutes and enjoy.