Preheat the oven to 350 degrees F. Grease and flour a 10-inch tube pan.
Sift the flour together with the baking powder, baking soda and salt in a bowl. Set aside.
In a large mixing bowl with an electric mixer, beat the butter and shortening together until creamy, about 2 minutes. Add the granulated sugar and beat 5 minutes more.
Add the eggs one at a time, beating only until the yolks disappear into the batter. Add the vanilla and lemon zest and juice.
Add the flour mixture alternately with the buttermilk, beginning and ending with the flour. Scrape the sides of the mixing bowl and beat only until well blended. Pour into the prepared pan and bake a toothpick comes out clean, about 1 hour 10 minutes. Let cool slightly, then turn the cake out of the pan while it is still warm onto a wire rack. Let cool completely.
Drizzle with Reba's Royal Glaze before serving.
Reba's Royal Glaze:
Mix together the confectioners' sugar, whisky, lime zest and juice and lemon zest and juice in a bowl. The glaze should be thick, yet pourable. Serve immediately.