• 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. Be sure not to over mix here.
• 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. This helps it stay put as the muffins bake.
• 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.
