preheat the oven to 350˚ and grease 8-inch loaf pans

in a stand mixer with the paddle attachment beat the butter and sugar until fluffy, about 5 minutes, scraping down the bowl halfway through

wash and zest the grapefruits, then juice the grapefruits

when the sugar is fluffy, add the eggs one at a time, beating afterward each addition

if you have an aluminum paddle on your mixer, take the bowl off and proceed by hand, if you have stainless steel OR a paddle with a spatula you can use the mixer to finish the pound cake

stir the zest in the eggs with a wooden spoon

in a smaller bowl mix the flour, baking soda, and baking powder together

mix the buttermilk and 1/4 of a cup of grapefruit juice

add 1/4 of the flour mix to the mixing bowl, follow it with 1/3 of the buttermilk mixture, repeat beginning and ending with the flour, stirring well after each addition

divide evenly between loaf pans

bake at 350˚ 40-50 minutes or until a toothpick comes out cleanly

let the loaves cool on a wire rack

when they're cool mix the two cups of powdered sugar with 2-3 Tablespoons of the leftover grapefruit juice for a glaze, start with the smallest amount adding small amounts until the glaze is thin enough to drizzle and thick enough to cling

pour on the loaves and let it set up

slice and serve