Prep. Set an oven rack in the lower third of the oven. Preheat the oven 325°F. Spray a 15-cup bundt pan (not a 12-cup!!) heavily with nonstick cooking spray.
Peaches. In a small pan, over medium heat, melt 1/4 cup butter. Add 1/2 cup brown sugar and continue to cook, stirring constantly,  until the sugar has dissolved about 1 minute. Transfer mixture even to the prepared bundt pan. Arrange peach pieces in a single layer on top of the brown sugar mixture.
 Flour. In a medium bowl, whisk flour (3 cups) and salt (1/2 teaspoon). 
 Dough. In the bowl of a stand-up mixer, beat the remaining 1 1/2 of butter for 2 minutes, on medium speed, or until it is light and fluffy. Scrape down sides, then add cream cheese and continue to beat, on medium, for 1 minute. Scrape down sides, then gradually add granulated sugar and remaining 1 1/2 cups brown sugar, beating on medium speed until light and fluffy, 3 to 5 minutes. Scrape down sides and add eggs (6 large), 1 at a time, beating just until yolk disappears. Beat in 1 teaspoon of vanilla. Scrape down sides and add to butter mixture alternately with 1/4 cup bourbon, beginning and ending with flour mixture.
 Bake. Pour evenly into the bundt pan. Tap on the counter to remove any air bubbles. Place bundt pan on a large rimmed baking sheet (half-sheet size) to catch any spills. Bake for 1 hour and 25 minutes, or until a skewer inserted into the center of the cake comes out clean. Allow it to cool in the pan set on a wire rack for 25 minutes. Invert the cake onto a wire rack and cool completely.
 Glaze. In a mixing bowl, whisk together powdered sugar (1 cup), vanilla (1/2 teaspoon), 1 tablespoon of milk, and 1 teaspoon bourbon. Add more milk as needed to reach drizzling consistency. Drizzle over cooled cake.