Step 1

Heat the oven to 400° F (200° C).

Step 2

In a small bowl, combine the flour, baking powder, cinnamon, salt, and brown sugar.

Step 3

In a separate bowl, whisk together the butter, egg yolk, milk, and vanilla.

Step 4

Stir the wet ingredients into the dry ingredients.

Step 5

Fold in the diced apples and chopped pecans.

Step 6

Transfer the batter to a lightly buttered 10-ounce ramekin.

Step 7

Combine the flour, brown sugar, cinnamon, chopped pecans, and softened butter in a small bowl until crumbly.

Step 8

Pour the streusel topping over the muffin batter and spread evenly over the top.

Step 9

Bake for 25-30 minutes or until a toothpick inserted into the center of the muffin comes out clean.

Step 10

Cool for 5 minutes on a wire rack and enjoy warm.