Preheat oven to 350ºF (180ºC).
Grease a large 10 to 12-cup bundt cake pan with soft shortening. Coat with flour, shaking off excess. Reserve.
In a large bowl, beat 1 ½ cups unsalted butter until creamy and gradually add 2 ½ cups sugar, beating for 3 minutes.
Add 5 eggs, one at a time, beating well after each addition.
Add 1 teaspoon vanilla extract and 2 teaspoons orange zest.
Sift together the dry ingredients: 2 ½ cups all-purpose flour, ½ cup rye flour and 1 teaspoon baking soda in a bowl. Or have them measured and sift them directly over the butter mixture when adding it.
Add the dry ingredients in 3 additions, alternating with ¾ cup milk and 3 tablespoons bourbon in two additions. Mix well but don't overbeat. I like to use a spatula to scrape the bottom a few times to make sure no dry ingredients are unincorporated.
Bake for 1 hour to 1 hour and 15 minutes or until a cake tester or toothpick inserted comes clean. Start checking at the hour mark as pans and ovens are different, and times might vary.
Transfer to wire rack and let cool for about 20 minutes. Make sure no cake is sticking to the center tube or sides. I use a smooth-bladed knife to carefully scrape them.
Invert the cake onto the wire rack.
Drizzle some of the caramel sauce over the warm cake. Serve with extra sauce.