Preheat your oven to 350°F (175°C) and prepare a 9x5 inch loaf pan by greasing it or lining with parchment paper.

In a medium bowl, whisk together the all-purpose flour, baking powder, baking soda, and salt until well blended.

In a large mixing bowl, combine the melted butter with granulated sugar, whisk until smooth, then add the eggs one at a time, incorporating fully before adding the next. Stir in vanilla extract and buttermilk.

Gradually add the dry ingredients to the wet mixture, stirring gently until just combined.

Fold in the red and green sprinkles gently to prevent bleeding.

Pour the batter into the prepared loaf pan, smooth top, and optionally sprinkle coarse sugar and additional sprinkles.

Bake for 45-55 minutes, checking for doneness with a toothpick.

Allow to cool in the pan for 10-15 minutes, then transfer to a cooling rack to cool completely.