FOR THE CRUMB TOPPING: – 1/3 cup (40g) all-purpose flour – 1/4 (50g) cup packed light brown sugar – 1 tablespoon (5g) unsweetened cocoa powder – 1/8 teaspoon ground cinnamon – pinch of salt – 2 tablespoons (28g) unsalted butter, cold and cut into small cube FOR THE MUFFINS: – 1 & 3/4 (210g) cups all-purpose flour – 3/4 (150g) cup granulated sugar – 1 teaspoon baking powder – 1/2 teaspoon baking soda – 1/4 teaspoon salt – 1/2 cup (122g) plain or vanilla yogurt – 1/4 cup (56g) unsalted butter, melted and slightly cooled – 2 large eggs, lightly beaten – 1/2 teaspoon vanilla (You can omit if using vanilla yogurt.) – 2 tablespoons (10g) cocoa powder