Gather the ingredients. Chop into big pieces 200 g semi-sweet chocolate + small pieces 100 g semi-sweet chocolate.
Chop 60 g pecans + 90 g pecans.
The Streusel Topping
In a small bowl, combine the 60 g all-purpose flour, 60 g brown sugar, 1/2 tsp. ground cinnamon and the melted 45 g unsalted butter. Mix with a fork until the mixture resembles coarse crumbs. Stir in the 60 g pecans and set aside.
The Dry
In a large bowl, combine the 125 g all-purpose flour, 30 g sugar, 1-1 ½ tsp. baking powder (more will create a more airy center), 1/4 tsp. salt, 1/4 tsp. ground cinnamon, 90 g pecans, and the remaining 100 g semi-sweet chocolate.
The Wet
In a small bowl, whisk together the 1 egg and 1/2 tsp. vanilla extract.
In a sauce pan, mix 200 g semi-sweet chocolate, 80 ml milk, and 55 g unsalted butter over low-medium heat.
Stir until the chocolate is melted and the mixture is smooth.
Stir in the egg mixture until well combined.
Pour the wet ingredient mixture into the dry ingredient mixture. Stir just until moistened; do not overmix.
The Muffins
Preheat your oven to 375°F (190°C). Line a 12-cup muffin tin with paper liners.
Spoon the batter into the prepared muffin cups, filling each approximately two-thirds full.
Sprinkle generously with the prepared streusel topping. Using a spoon, you can apply slight pressure to make them fit.
Bake for 20 to 25 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
The Serving
Let the muffins cool in the pan for 5 minutes before carefully removing them to a wire rack to cool completely. Chocolate Streusel Pecan Muffins [Muffins au chocolat et aux pacanes].