Preheat the oven to 375° F and grease and flour a 9×13 pan or a 15x10x1-inch jellyroll pan.
In a small pan on low heat, melt the butter with the Ruby Red grapefruit juice and water.
Mix together the flour, sugar, baking soda, cinnamon and salt. Stir in the pecans and grapefruit zest. Pour in the melted butter, along with the buttermilk, eggs and vanilla extract. Mix until a smooth batter is formed.
Pour the batter into the greased and floured pan, and bake for 25-30 minutes, checking it at 20 minutes, or until the cake is lightly browned and an inserted knife or toothpick comes out clean. (If using a jellyroll pan, it should take about 20 minutes, so check it at 15 minutes.)
As the cake cools, prepare the frosting. Cream together the cream cheese, butter, grapefruit juice, grapefruit zest, vanilla extract. Stir in the sugar and blend until smooth. Once the cake is cool to the touch (about an hour or so), frost the cake.
Ruby red grapefruit and pecan sheet cake | www.homesicktexan.com