Position oven rack in the lower middle position; preheat to 350°; prepare Bundt pan by making a paste from 1 tablespoon melted butter and 1 tablespoon flour; apply it with a pastry brush so you can thoroughly coat the surface of the pan, including all the nooks and crannies.
Nut filling: Toss all the filling ingredients together in a bowl.
Cake: Whisk the flour, salt, baking powder, and baking soda together in a bowl; in a small bowl, whisk buttermilk, molasses, bourbon, and vanilla together.
In a big bowl, beat the butter and sugar together with an electric mixer on medium speed until light and fluffy--3 to 6 minutes.
Beat in the eggs and egg yolk, one at a time, until combined, about 1 minute.
Decrease mixer speed to low; beat in 1/3 of the flour mixture, followed by half of the buttermilk mixture; repeat with half the remaining flour mixture and the remaining buttermilk mixture.
Beat in the remaining flour mixture until just incorporated.
Scrape half the batter into the prepared pan, smooth the top; sprinkle evenly with the nut filling.
Scrape the remaining batter over the nuts and smooth the top.
Wipe any drops of batter off the sides of the pan and gently tap the pan on the counter to settle the batter.
Bake the cake until a wooden pick comes out with a few moist crumbs attached, 50-60 minutes, rotating pan halfway through baking.
Let cake cool in the pan for 10 minutes, then turn out onto a wire rack; let cake cool completely, about 2 hours.
Glaze: Whisk all the glaze ingredients together until smooth, then let sit until thickened, about 25 minutes.
Drizzle the bourbon glaze over the top and sides of the cake; let glaze set, about 25 minutes, before serving.