Set oven to 325°F (163°C). Grease and flour a Bundt or tube pan.
In a large bowl, beat softened butter, vegetable shortening, and sugar with a mixer for 3–5 minutes until light and fluffy.
Add eggs one at a time, mixing well after each. Scrape down the bowl as needed.
In a separate bowl, whisk together flour, baking powder, and salt.
Gradually add the flour mixture to the creamed butter, alternating with milk. Start and end with the dry mix. Mix just until combined.
Stir in vanilla extract until fully blended. Pour batter into the prepared pan. Smooth the top and tap gently to release air bubbles.
Bake for 75–85 minutes. A toothpick inserted into the center should come out clean. Let it cool in the pan for 10–15 minutes. Then, turn it out onto a wire rack to cool completely.