Place your raspberries in a single layer on a plate or small sheet pan and put them in the freezer for about 20 minutes. This will keep them from breaking apart while mixing.

Preheat oven to 425°F and grease 6 wells of your muffin pan. Melt your butter and leave aside to cool.

In a medium bowl, use a fork to mash your banana. Add your egg, yogurt, and vanilla and mix well.

Sprinkle your flour, sugar, baking powder, baking soda, and salt evenly over the top of your wet ingredients. Use your spatula to kind of mix those dry ingredients together, then dig in and begin incorporazting them into the wet ingredients.

When you are halfway through mixing, drizzle in your melted and cooled butter. Continue mixing until there are only a few streaks of visible flour. Fold in your frozen raspberries, leaving aside about 6 to 8 berries. Cut those in half for garnishing.

Scoop your batter evenly into the prepared muffin pan. Top each muffin with 2 or 3 raspberry halves, with the pretty parts up. Sprinkle each muffin with about a teaspoon of raw or coarse sugar.

Bake at 425°F for 5 minutes. Without opening the oven, turn down the temperature to 350°F and continue baking for 15 to 18 minutes, or until a skewer inserted into a muffin comes out clean or with just a few moist crumbs.

Let cool for 5 minutes in the pan, then remove to a wire rack to cool for 10 more minutes.