Preheat the oven to 350°F (180°C) and position the rack in the center. Grease a 10- or 12-cup Bundt or metal tube pan, or two 6-cup Bundt pans.
In a medium bowl, sift and hand whisk flour, baking powder, soda, and salt for thorough mixing.
Using a stand mixer with a paddle attachment, beat butter and sugars on medium-high for about 5 minutes until fluffy. Pause the mixer to scrape sides with a spatula. Add eggs one at a time.
In a small bowl, combine bourbon and buttermilk. With the mixer on low, add flour in 3 parts, alternating with buttermilk-bourbon mixture in 2 parts, starting and ending with flour. Mix briefly after each addition and finish blending by hand for a smooth, shiny batter.
Pour batter into the prepared pan and bake until golden and springy, 40-45 minutes for a 10- or 12-cup Bundt, and 30-35 minutes for a 6-cup Bundt.MAKE THE GLAZE
In a saucepan over low heat, melt butter and sugar with bourbon. Whisk to combine.
Remove the cake from the oven, leave it in the pan, and poke holes with a skewer. Pour 3/4 of the glaze over the cake, reserving the rest. Cool for 30 minutes.
Invert the cake onto a stand or plate, remove the pan, and optionally brush with the remaining glaze. Slice and serve.