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

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

In a large mixing bowl, whisk melted butter and granulated sugar until creamy, then add eggs one at a time, followed by vanilla and buttermilk.

Gradually fold in the dry mixture until just combined; do not overmix.

Fold in the red and green sprinkles until evenly distributed.

Pour batter into prepared loaf pan, smoothing the top, and sprinkle with coarse sugar if desired. Bake for 45-55 minutes until a toothpick comes out clean.

Remove from oven, let cool in the pan for 10-15 minutes, then transfer to a wire rack to cool completely before slicing.