Step 1

Heat oven to 350° F (177° C)

Step 2

Grease a 5-inch baking dish with ½ tablespoon of butter. Place baking dish on top of a baking sheet.

Step 3

In a medium-sized mixing bowl, beat the butter and sugar at a moderate speed with hand mixer for 1 minute.

Step 4

Mix in the egg, grapefruit juice, zest, and vanilla.

Step 5

In a separate small bowl, whisk together the flour, baking powder, and salt. Add to the butter/sugar mixture and mix at low speed to combine.

Step 6

Stir in the milk.

Step 7

Pour batter into a lightly buttered baking dish and bake for 40-45 minutes or until top is golden.

Step 8

Remove the cake from the oven and allow to cool, 10 minutes.

Step 9

While the cake is cooling, make the glaze: In a small bowl, whisk together the powdered sugar and grapefruit juice until smooth.

Step 10

Using a toothpick, the tip of a sharp knife, or the tines of a fork, poke holes all over the cake.

Step 11

Pour the glaze over the cake.

Step 12

Slice and enjoy.