Preheat oven to 325 F.
Grease and flour a bundt pan. Set aside.
In a large bowl whisk together flour, baking powder, and salt. Set aside.
In a large bowl cream together butter, shortening, and sugar.
Mix in eggs, one at a time, mixing thoroughly after each egg.
Mix in egg yolks.
Mix in vanilla extract, lemon extract and butter flavoring (if using)
Add dry ingredients into wet ingredients, alternating with the milk and buttermilk.
Mix until batter is fluffy.
Spoon batter into prepared pan and shake the pan to even out the top and release any air bubbles.
Bake for 1 hour and 20 mins. ( Check it at the 1-hour mark. Do not over-bake as cake will continue to cook as it cools)
Remove from oven and let the cake sit in the pan for about 10 minutes.
Then remove from pan and place on a cooling rack to finish cooling.
Slice and serve!