Set oven to 350º F.
In a small bowl, rub two tablespoons of butter together with 3 tablespoons of flour until it becomes a paste. Rub the paste into every crevice of the bundt pan possible. Make sure the entire pan is covered. This will help your bundt cake to come out in one piece.
In a medium bowl, whisk the flour, salt, baking powder, and baking soda together.
In a separate, larger bowl, cream the butter and sugar together on high for 3-4 minutes until light and fluffy. Do this using either a hand mixer or the paddle attachment of your stand mixer.
One by one, add the eggs and the egg yolk, making sure each is incorporated fully before adding the next. When all the eggs are incorporated, add the vanilla.
Add ⅓ of the dry ingredients to the bowl, and mix until just incorporated.
Now, add ½ of the buttermilk to the batter and mix until that is combined. Repeat, alternating adding wet and dry until you run out, you should end the rotation by adding the last ⅓ of flour. MAKE SURE NOT TO OVERMIX YOUR DOUGH.
When the last of the flour mixture is just incorporated and no flour streaks remain, add the bourbon whiskey and stir quickly to evenly disperse it through the batter.
Pour your batter into your prepared pan and bake for 40-50 minutes or until a toothpick inserted into the center comes out clean.
Let cool for at least 1 hour before attempting to remove from pan.