Preheat Oven: Set oven to 425°F (220°C). Line muffin tins or grease well.

Make Streusel: Combine flour, sugars, cinnamon, and pumpkin pie spice. Cut in cold butter using a fork or pastry cutter until crumbly. Chill until ready to use.

Cream Butter & Sugars: In a large bowl, cream butter, granulated sugar, and brown sugar until fluffy (about 2 minutes).

Add Eggs & Wet Ingredients: Beat in eggs one at a time, then add vanilla, pumpkin puree, and mashed banana. Mix until just combined (it may look curdled—this is normal).

Combine Dry Ingredients: In another bowl, whisk flour, baking soda, baking powder, cinnamon, pumpkin pie spice, and salt.

Mix Batter: Gradually mix dry ingredients into wet until just incorporated. Do not overmix.

Fill Muffin Tins: Fill muffin liners ¾ full (or to the top for bakery-style muffins). Top generously with streusel.

Bake:

Bake at 425°F for 5 minutes.

Without opening the oven, reduce temperature to 350°F (175°C).

Bake:

13–15 minutes for regular muffins

20–25 minutes for jumbo muffins

10–14 minutes for mini muffins

Muffins are done when a toothpick comes out clean.

Cool & Glaze: Cool on wire racks. If using, whisk glaze ingredients and drizzle over cooled muffins.