Preheat the Oven: Preheat your oven to 350°F (175°C). Prepare a 9 × 5-inch loaf pan by either lightly greasing it or lining it with parchment paper to ensure easy removal after baking.
Combine the Dry Ingredients: In a medium mixing bowl, thoroughly whisk together the all-purpose flour, baking powder, baking soda, and salt. Set aside once the mixture appears evenly blended and free of clumps.
Prepare the Wet Mixture: In a large mixing bowl, whisk the melted butter and granulated sugar together until the mixture achieves a smooth and glossy consistency. Incorporate the eggs one at a time, whisking gently after each addition. Once the eggs are fully combined, stir in the vanilla extract and buttermilk until the mixture becomes cohesive and uniform in texture.
Combine Wet and Dry Ingredients: Gradually add the dry mixture to the wet ingredients, stirring carefully until just combined. Avoid overmixing, as this may result in a dense texture rather than the desired soft and tender crumb.
Incorporate the Sprinkles: Using a silicone spatula or wooden spoon, gently fold in the red and green sprinkles, ensuring they are evenly distributed throughout the batter. Exercise caution to prevent excessive mixing, which could cause the colors to bleed.
Transfer and Garnish: Pour the batter evenly into the prepared loaf pan, smoothing the surface with the back of a spoon or an offset spatula. If desired, sprinkle coarse sugar and additional sprinkles over the top to enhance both texture and visual appeal.
Bake the Bread: Place the loaf in the preheated oven and bake for 45–55 minutes, or until a toothpick inserted into the center emerges clean. Baking times may vary slightly depending on oven type and altitude.
Cooling and Serving: Allow the bread to cool in the pan for 10–15 minutes before transferring it to a wire rack to cool completely. Once cooled, slice the loaf using a serrated knife and serve at room temperature for optimal texture and flavor.