Preheat oven to 325 degrees Fahrenheit. Butter and sugar a 10 inch-12 cup tube pan. Please read the Special Note at the end of the recipe.
Beat butter and shortening at medium speed until fluffy and creamy.
Gradually add sugar, beating at medium speed until light and fluffy.
Add eggs, 1 at a time, beating until egg yolk is blended well after each addition
Sift together flour, baking powder, and salt. Add to the butter mixture alternately with the milk, beginning and ending with flour. Beat at a low speed until well-blended after each addition.
Stir in vanilla, lime zest, and lime juice. Stir until well blended. Pour the batter into a buttered and sugared 10-inch-12 cup tube pan
Place in the oven and bake for 1 hour and 15 to 30 minutes or until a long toothpick or cake tester is inserted into the center of the cake comes out clean, When the toothpick or cake tester comes out clean, the cake is done. Let cake rest in the cake pan for 10-15 minutes then carefully invert onto a cooling rack to completely cool.
Key Lime Glaze: Combine the powdered sugar, fresh lime juice, and vanilla extract. Mix until smooth. Brush the Key Lime Glaze on the cake while it is warm. Note: You may not use all the glaze.
Special Note: One of the great things about baking is that you can always make any recipe your own. That said, this pound cake is great without the glaze. This is my preferred way to serve it. By buttering and sugaring the cake pan, I get the sweet crunchy pound cake crust that I love. The sweet, sugary crust makes the glaze unnecessary. If you choose to use the glaze, may I suggest you grease and flour the cake pan? This would reduce the chance of the pound cake becoming too sweet. Have fun with this cake and experiment. Make it yours!