Preheat oven to 425°F (218°C). Spray a 12-count muffin pan with nonstick spray or line with cupcake liners. You may need a 2nd pan as this recipe makes up to 14 muffins, though you can always bake in batches using 1 pan. Set aside. *See note about jumbo size & mini muffins.*

Mix the brown sugar, granulated sugar, and cinnamon together in a medium bowl. Stir in the melted butter, and then gently mix in the flour using a fork. Keep the mixture as large crumbles and do not over-mix. If over-mixed, this will turn into a thick paste. Set topping aside.

Whisk the flour, baking soda, baking powder, cinnamon, and salt together in a large bowl. Set aside.

Using a handheld or stand mixer fitted with a paddle attachment, beat the butter and both sugars together on high speed until smooth and creamy, about 3 minutes. (Here’s a helpful tutorial if you need guidance on how to cream butter and sugar.) Scrape down the sides and bottom of the bowl as needed. Add the eggs, yogurt, and vanilla extract. Beat on medium speed for 1 minute, then turn up to high speed until the mixture is combined and mostly creamy. (It’s ok if it appears somewhat curdled.) Scrape down the sides and bottom of the bowl as needed. With the mixer running on low speed, add the dry ingredients and milk into the wet ingredients and beat until no flour pockets remain. Fold in the apples.

Spoon the batter evenly into each cup or liner, filling each all the way to the top. Spoon crumb topping on each, gently pressing it down so it sticks.

Bake for 5 minutes at 425°F, then, keeping the muffins in the oven, reduce the oven temperature to 350°F (177°C). Bake for an additional 15–18 minutes or until a toothpick inserted in the center comes out clean. The total time these muffins take in the oven is about 20–23 minutes. Allow the muffins to cool for 5 minutes in the muffin pan, then transfer to a wire rack to continue cooling.

Whisk all of the icing ingredients together and drizzle over warm or cooled muffins.

Iced or plain muffins stay fresh covered at room temperature for a few days or in the refrigerator for up to 1 week.