Put the buttermilk in a small bowl and add the poppy seeds, grapefruit juice, and zest. Stir to combine and set aside.
Cream the butter and sugar together until fluffy. Beat in the eggs, one at a time.
Whisk together the dry ingredients in a separate bowl.
Add the dry ingredients to the creamed butter mixture, alternating with the buttermilk mixture. Add about 1/3 of the flour, then 1/3 of the buttermilk, and continue until everything is well combined.
Spread the batter in the bundt pan. Smooth the top slightly to make sure it is even.
Bake for about 50 minutes, until the top is risen and golden, and a toothpick inserted in the center comes out without wet batter clinging to it.
Let the cake cool for about 10 to 15 minutes and then loosen the cake all the way around the pan and invert it onto a plate. If you have trouble removing it, rap the bottom of the pan sharply on a firm surface and try again.
Flip the cake back over so the risen side is up. Make little holes with a skewer all over the top and then spoon the fresh juice all over the top, letting the juice seep into the cake. Do this slowly so the juice has a chance to soak in.
When the cake is completely cool. pour the glaze over it, and enjoy.
https://theviewfromgreatisland.com/grapefruit-poppy-seed-cake/ February 23, 2015