Preheat oven to 350 and grease two four inch round cake pans or one eight inch round. Set aside. Line bottom with parchment circles if desired.
Sift together the dry ingredients in a medium size bowl. In another bowl, beat together the butter, peanut butter and brown sugar until light and fluffy. Add egg and vanilla and beat until smooth.
Add the buttermilk and dry ingredients alternately, beating well after each addition. Pour batter into prepared pan filling it three-quarters full and bake for 25 minutes, or until the sides of the cake begin to pull away from the pan and a cake tester inserted into the center comes out clean. Turn over onto a large plate and let cool while you make the frosting.
Make the frosting. Chop the chocolate and butter and set aside.
In a saucepan, bring the sugar and heavy cream to a boil over medium heat. Reduce the heat to low and simmer for 6 minutes. Do not let the saucepan overflow.
Remove from heat and stir in the chocolate and butter until melted.
Stir in the vanilla extract. Let the frosting cool completely, whisking occasionally during cooling. Once completely cool at room temperature, the frosting will be spreadable. {note: I chilled my frosting in the refrigerator, whisking frequently, to speed up the cooling.}
If making a mini layer cake, slice each layer in half horizontally (a good trick, that I did not know about, is to stick toothpicks all around the cake as markers to help you cut evenly). I’ve also read that a cake chilled in the freezer is easier to slice.
Frost cake. Sprinkle the frosted cake with finishing salt. Transfer cake to serving plate using a spatula. Turn a beer chalice upside down. Set plate on top.
Stay classy.