In a medium mixing bowl, combine the flour, sugar, cinnamon, and salt. Stir in the melted butter, mixing just until combined. Set aside while you prepare the rest of the recipe.

Preheat oven to 400°F (204°C). Line a 12 cup muffin tin with paper liners and set it aside.

In a large mixing bowl, combine the flour, baking powder, nutmeg, and salt. Set aside.

In the bowl of a stand mixer fitted with the paddle attachment, or in a large bowl using a handheld electric mixer, combine the butter and both sugars and beat on medium-low speed until light and fluffy; about 3 minutes. Add in the orange zest and beat until combined.

Add in the eggs and yolk, one at a time, beating well after each addition. Slowly beat in the vanilla and milk.

Reduce mixer speed to low and gradually add in the dry ingredients, mixing just until combined.

Turn mixer off. Using a rubber spatula, gently fold the chocolate chunks and raspberries into the batter until combined.

Divide batter evenly among prepared muffin cups.

Crumble up the topping and evenly distribute it on top of the 12 muffins, piling it high in the center.

Gently push the streusel into the batter.

Bake for 20 to 22 minutes, or until the tops are lightly golden brown and a toothpick inserted in the middle comes out clean.

Allow the muffins to cool in the pan, placed on top of a wire rack, for 10 minutes, then transfer them to a large serving plate.