Position oven rack in the lower-middle position; preheat to 350 degrees.
Prepare Bundt pan using the following method—make a paste from 1 tablespoon melted butter and 1 tablespoon flour ; apply it with a pastry brush, you can thoroughly coat the surface of the pan, including all the nooks and crannies.
In a big bowl, whisk the flour, salt, baking powder, and baking soda together.
In a small bowl, whisk the buttermilk and vanilla together.
In another big bowl, beat the butter, sugar, and peanut butter together with an electric mixer on medium speed until light and fluffy, 3-6 , minutes.
Beat in the eggs and egg yolk, one at a time, until combined, about 1 minute.
Decrease speed to low and beat in 1/3 of the flour mixture, followed by half of the buttermilk mixture.
Repeat with half of the remaining flour mixture and the remaining buttermilk mixture.
Beat in the remaining flour mixture until just incorporated.
Scrape the batter into prepared pan; 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 inserted in the center comes out with a few moist crumbs attached, 50-60 minutes, rotating the pan halfway through baking.
Let the cake cool in the pan for 10 minutes, then flip it out onto a wire rack; let cool completely for about 2 hours.
Make the glaze: whisk all glaze ingredients together in a bowl until smooth and let sit until thickened, about 25 minutes.
Pour the glaze over the top of the cake after it has cooled completely, letting the glaze drip down the sides.
Let the glaze set before serving, about 25 minutes.