Preheat the oven to 325°F (163°C). Line a loaf pan with parchment paper or grease it lightly with some of the melted butter from the ingredient list. If you want the nuts toasted, spread the 1/4 cup nuts on a small baking sheet and toast in the preheating oven, watching closely, until fragrant and lightly browned; set toasted nuts aside to cool.

In a large bowl, mash the 3 very ripe bananas with the back of a fork until mostly smooth.

Add the 1/3 cup melted unsalted butter, 1 tsp vanilla extract, and the 2 whisked eggs to the mashed bananas. Stir gently until just combined.

In a separate medium bowl, whisk together the dry ingredients: 1 3/4 cups flour, 1/2 cup sugar, 2 3/4 tsp baking powder, 1/2 tsp salt, 1 tsp cinnamon, and 1/4 tsp nutmeg until evenly mixed.

Add the dry ingredients to the wet banana mixture. Stir with a fork or spatula until just combined and no large streaks of flour remain—do not overmix.

Gently fold in the 1 cup blueberries with a spatula, taking care not to crush them (if using frozen blueberries, you may fold them in frozen).

Transfer the batter to the prepared loaf pan and smooth the top. Sprinkle the 1/4 cup nuts (toasted or raw, per your choice) evenly over the top.

Bake in the preheated 325°F oven for 60–75 minutes, until the top is golden and a toothpick inserted into the center comes out clean or with only a few moist crumbs. If you used frozen blueberries, plan on adding about 5–10 extra minutes of baking time.

Remove the loaf from the oven and let it cool in the pan for 15 minutes. Be careful—blueberries and the interior will be very hot.

After 15 minutes, lift the bread from the pan (using the parchment if lined) and transfer it to a wire cooling rack to cool completely or slice and serve warm.

Store any leftovers in a covered container at room temperature for 2–3 days.