Cake
2 cups all-purpose flour
1 3/4 teaspoons baking powder
1 teaspoon kosher salt
1 2/3 cups granulated sugar
1 tablespoon grapefruit zest
2 large eggs, at room temperature
1 cup whole milk, at room temperature
3/4 cup canola oil
1 teaspoon vanilla extract

Syrup
1 cup grapefruit juice
2/3 cup granulated sugar

Glaze
3/4 cup confectioners' sugar
1 tablespoon plus 1 teaspoon grapefruit juice