Preheat the oven to 350°F. Spray a 9x5-inch loaf pan with nonstick cooking spray and set aside.
In a medium bowl, whisk together the flour, baking powder, baking soda, cinnamon, and salt.
In a separate large bowl or stand mixer, beat the softened butter and granulated sugar until light and fluffy.
Add the eggs, vanilla extract, sour cream, and milk. Mix until just combined.
Add the dry ingredients to the wet ingredients and gently stir with a spatula or wooden spoon until just combined. Do not overmix.
Gently fold in ½ cup of the Christmas sprinkles, being careful not to overmix so the colors do not bleed into the batter.
Pour the batter into the prepared loaf pan and spread it evenly. Bake for 60–70 minutes, or until a toothpick inserted into the center comes out clean. If the top begins to brown too quickly, loosely tent the pan with foil.
Let the bread cool in the pan for 10 minutes, then carefully transfer it to a wire rack to cool completely.
To make the glaze, whisk together the powdered sugar, milk, and vanilla extract until smooth.
Spread the glaze over the completely cooled bread and top with the remaining ¼ cup of Christmas sprinkles.
Slice and serve.
Notes
If the top of the bread begins to brown before the center is fully baked, loosely tent the loaf pan with aluminum foil and continue baking until a toothpick inserted into the center comes out clean.Store the bread in an airtight container at room temperature for up to 3 days.