Preheat the oven to 350°

Generously spray a 12-cup Bundt pan with non-stick spray, and dust with flour or spray with cooking oil and flour spray.

Onto a big piece of wax paper sift together the cake flour, baking powder, and the salt. Or you can sift it into a bowl.

In a large bowl with an electric mixer, cream the butter and sugar together on medium-high speed until pale and fluffy (about 5 minutes).

Beat in the eggs, one at a time, until incorporated.

Scrape the bottom and sides of the mixing bowl and beat briefly again.

Add the grated ruby red grapefruit zest, and ruby red grapefruit juice, mixing on medium speed until combined.

Add the ½ the sifted flour mixture, mixing on medium speed until just barely incorporated.

Add the sour cream, reserving 1 tablespoon for the glaze and just stir until mixed through.

Stir in the remaining flour, mixing until it has just thoroughly mixed. Be careful not to over mix. But you want it to all be incorporated.

Transfer the batter to the prepared Bundt pan.

Drop the pan from a couple of inches onto a countertop. To remove any large air pockets.

Bake for 60 to 65 minutes, or until a cake tester inserted into the thickest part of the cake comes out clean or with a few moist crumbs.

Have a rack over a catch pan or a rimmed cookie sheet ready.

Cool in the pan for 20 minutes, then invert onto a wire rack to cool completely.

While the cake is cooling, heat the ruby red grapefruit juice with the sugar on medium heat in a small saucepan or the microwave in a measuring cup until the sugar has dissolved. Maybe 30 seconds to a minute, stirring occasionally.

When you invert the cake onto a rack, brush the 1st glaze all over the cake. Let the cake absorb all the glaze, picking up any leftover glaze that has dripped onto the catch pan and brush again to incorporate as much glaze as possible.

Let the cake cool completely.

When the cake has completely cooled, mix together the 2nd glaze ingredients and pour over the cooled cake, letting the glaze drip over the sides.