Heat the oven to 325°F. Butter a 9 inch by 5 inch loaf pan, line the bottom with parchment paper, and butter the paper.
Sift or whisk the flour, baking powder, and salt together into a medium bowl.
1⅞ cup (227 grams) cake flour, ½ teaspoon baking powder, ½ teaspoon salt
Cream the butter and sugar together until it is light in color and fluffy, about 5 to 7 minutes. Scrape down the bowl.
16 tablespoons (227 grams) unsalted butter, 1 cup plus 2 tablespoons (227 grams) granulated sugar
Add the eggs one at a time and beat on medium for one minute between each addition, scraping down the bowl as necessary.
4 large eggs
Beat in the vanilla. Add the dry ingredients and mix in on low or stir in by hand just until mixed, then stir in the rainbow sprinkles.
1 tablespoon vanilla extract, ½ cup rainbow sprinkles
Transfer the cake batter to the prepared loaf pan and give it a few thwacks on the countertop to even it out.
Bake for 65 to 70 minutes in the lower third of the oven for 80 to 90 minutes until the top is a light brown and a toothpick inserted into the cake comes out clean. Check the cake at about 40 minute and cover it with foil if the cake is browning too quickly.
Let the cake cool in the pan for 10 minutes before removing from the pan onto a rack. Let the cake cool completely before glazing.
To make the glaze, put the powdered sugar into a small bowl. Add two tablespoons of the milk or other liquid you are using and stir. If the glaze is too thick, add a bit more liquid, a teaspoon at a time. You want the glaze to be pourable and drip but not run right off the cake.
2 cups (230 grams) powdered sugar, 2 to 3 tablespoons vanilla
If there is no dairy in the glaze, you can store the funfetti pound cake at room temperature, well-wrapped, for up to one week.