In a small bowl, combine flour, brown sugar, granulated sugar, and cinnamon with a whisk.
Add the melted butter and mix with a fork until the consistency reaches wet sand and set aside.
Preheat the oven to 425°F. In a large mixing bowl, combine boxed cake mix, pumpkin puree, eggs, yogurt, vegetable oil, and pumpkin pie spice.
With an electric handheld mixer, beat on low speed until combined. Scrape down the sides and bottom of the bowl with a spatula to ensure no more streaks of flour remain.
Next, divide and fill the muffin batter evenly into eighteen paper-lined muffin tin cups using a ¼ cup cookie scoop.
Crumble one to two tablespoons of the butter-sugar crumb mixture onto each muffin top. Then very lightly press the crumb into the top of the muffin batter.
Bake the muffins for seven minutes at 425°F, then lower the oven temperature to 350°F. Do not open the oven door when lowering the temperature. Continue baking for ten more minutes or until a toothpick comes out clean when inserted into the middle.
Remove the pumpkin muffins from the oven and allow them to cool in the muffin tray for three to five minutes. Then, remove the muffins by holding the paper liners and continue to cool completely on a wire rack. Store the muffins in an airtight container in the refrigerator for up to four days.