In a small saucepan, cook the butter over medium heat until brown and fragrant. When brown specks (not black!) collect at the bottom of the pan, immediately transfer the butter to a small bowl. Let cool to room temperature.
Preheat the oven to 350ºF. Line the bottom of an 8 x 4-inch baking pan with parchment paper. Grease and flour the insides.
In a medium bowl, beat the brown butter, brown sugar, eggs, vanilla and buttermilk until smooth.
Stir in the flour mixture in two additions. Mix just until combined. A few lumps are okay.
Transfer the batter to prepared baking pan. Bake until the top is deep golden brown and q toothpick inserted into center comes out clean, about 38-43 minutes.
Let the bread cool in pan for 10 minutes, them turn it out onto a cooling rack to cool completely. Top with two coats of butterscotch glaze.
Butterscotch Glaze
Melt the butter in a small saucepan over medium heat. Stir in the brown sugar and salt.
Continue stirring over medium heat until the mixture comes to a boil. Boil for two minutes.
Turn the heat down and slowly stir in the heavy cream. Keep stirring until mixture is smooth. Remove from heat and stir in the vanilla extract.
Transfer the butterscotch glaze to a small bowl and let cool until thickened.