01 -
Preheat the oven to 400°F (200°C). Line a 12-cup muffin tin with paper liners and set it aside.
02 -
In a large bowl, sift together the flour, baking powder, nutmeg, cinnamon, and salt; set aside.
03 -
In a separate large bowl, whisk together the melted butter, both sugars, eggs, vanilla extract, sour cream, and mashed bananas until fully incorporated.
04 -
Add the dry ingredients to the wet mixture and, using a rubber spatula, mix until just combined. Avoid overmixing to prevent dry muffins.
05 -
Gently fold in the blueberries and walnuts until just incorporated.
06 -
Divide the batter evenly among the prepared muffin tins, filling each tin all the way to the top. Press a few extra blueberries onto the tops of each muffin and sprinkle with sparkling sugar, if desired.
07 -
Bake on the middle rack for 24 to 26 minutes, or until the tops are golden brown and a toothpick inserted into the center comes out clean, or with a few moist crumbs.
08 -
Cool the muffins in the pan for at least 15 minutes before serving warm or transferring to a cooling rack.