1 cup butter
1 cup shortening
2 cups white sugar
5 eggs
3 cups all-purpose flour
1/2 teaspoon baking powder
1/2 cup milk
1 1/2 teaspoons vanilla extract
1/2 cup key lime juice

1/4 cup white sugar
1/4 cup butter
3 tablespoons key lime juice

Preheat the oven to 325 degrees F (165 degrees C). Grease and flour a 10 inch tube pan.
In a large bowl, beat 1 cup of butter, shortening and 2 cups of sugar until light and fluffy. Beat in the eggs, one at a time, blending each one thoroughly. Combine the flour and baking powder, stir into the batter alternating with the milk, vanilla and 1/2 cup of key lime juice. Pour into the prepared pan and smooth the top.
Bake in the preheated oven until a knife inserted into the crown of the cake comes out clean, about 90 minutes.
While the cake is baking, make the glaze in a small bowl. Stir together 1/4 cup sugar, 1/4 cup butter and key lime juice. When the cake is done, invert it onto a wire rack while still warm, but not straight out of the oven. Poke several times with a skewer or toothpick. Pour the glaze over the warm cake allowing it to seep into the holes. Allow the cake to cool completely before serving.

Source: allrecipes.com