Preheat oven to 350°F. Grease 2 9" cake pans and line with parchment paper.
In a medium mixing bowl sift together the flour, baking soda and salt. Set aside.
In a mixing bowl or with a stand mixer (paddle attachment), cream butter, peanut butter, and sugar until light and fluffy. Then add eggs 1 at a time.
On the slow setting mix together dry ingredients into wet ingredients. Alternate dry and ingredients and buttermilk until fully combined. It will be light and fluffy.
Add evenly into both cake pans. Cook for 25-30 minutes or until the toothpick comes out clean. Let cool completely.
To make the frosting: Add butter, peanut butter and ⅓ cup heavy cream. Mix at low-speed until combined. Once completely combined add sugar.
Once cake is completely cool, frost the cake and serve at room temperature.
