1. Preheat your oven to 425°F and line a 12-cup muffin tin with paper liners or grease with butter.

2. Make the streusel topping first: In a small bowl, combine flour, brown sugar, cinnamon, and salt. Add cold, cubed butter and use your fingers or a pastry cutter to work it in until the mixture resembles coarse crumbs with some larger butter pieces. Set aside.

3. Prepare your apples: Peel and dice apples into small, even pieces (about 1/4-inch). Toss with 1 tablespoon flour to prevent sinking. This is crucial for even distribution!

4. Mix dry ingredients: In a large bowl, whisk together flour, baking powder, cinnamon, salt, and nutmeg.

5. Combine wet ingredients: In another bowl, whisk melted butter with both sugars until combined. Add eggs one at a time, then sour cream and vanilla. Mix until smooth.

6. Gently combine: Pour wet ingredients into dry ingredients. Gently fold together until just combined – you should still see some flour streaks. Do not overmix!

7. Fold in apples: Add floured apple pieces and fold gently until evenly distributed.

8. Fill muffin cups: Divide batter among muffin cups, filling them almost to the top (about 3/4 full) for those beautiful high domes.

9. Add streusel: Generously top each muffin with the streusel mixture.

10. Bake using the bakery secret: Bake at 425°F for 5 minutes, then reduce heat to 375°F (without opening the door) and continue baking for 15-20 minutes until tops are golden and a toothpick inserted in center comes out clean or with just a few moist crumbs.

11. Cool properly: Let muffins cool in the pan for 5 minutes before transferring to a wire rack.