Double Chocolate Banana Muffins

3/4 cup (165 g) light brown sugar, packed (I use 1/2 cup)
8 tablespoons (113 g) butter (or 1/3 cup (75 g) avocado or olive oil)
¼ cup (50 g) granulated sugar
1 tablespoon real vanilla extract
2 large eggs
½ cup (43 g) unsweetened cocoa powder
1 cup (227 g) ripe bananas (about 3 medium bananas; mashed)
1/3 cup (80 g) sour cream (I use full fat plain yogurt)
1 3/4 cups + 1 tablespoon (246 g) all-purpose flour
2 teaspoons baking powder
1 teaspoon baking soda
1 1/2 teaspoons sea salt
2/3 cup (160 g) whole milk
1 cup (170 g) dark chocolate chips (reserve about 1/3 cup (57 g) for the tops of the muffins)

Preheat the oven to 425°F (temperature will later reduce to 350-F).
Line a muffin pan with paper liners or thoroughly grease the pan.
In a large mixing bowl mix mashed banana and sour cream.
Add brown sugar, cooled melted butter, sugar, and vanilla. Mix until well combined.
Add cocoa powder and mix well.
Add eggs and mix well.
In a separate bowl, mix together flour, baking powder, baking soda, and salt.
Add the flour mixture to the wet mixture. Mix until the flour is barely incorporated.
Add milk and mix together until just combined.
Fold in the chocolate chips, reserving a handful for the tops.
Evenly distribute the batter into muffin cups. The batter will be heaping.
Sprinkle the reserved chocolate chips over the tops of the muffins.
Bake for 10 minutes in the center of the oven and then reduce the heat to 350℉ and bake for another 10 minutes, or until an internal temperature of 200°F is reached. When done, the tops will be puffed up tall; they should also bounce back when gently pressed in the center.
Allow to cool in the muffin pan for 5-10 minutes, then use a butter knife to gently get the warm muffins out of the pan before transferring them to a wire rack to finish cooling.