Preheat oven to 325°F (170°C). Spray a 9-inch round cake pan with baking spray with flour. Line bottom of pan with parchment paper.

In a medium bowl, whisk together flour, baking powder, salt, and baking soda.

In a large bowl, whisk together brown sugar, peanut butter, oil, and honey until combined and creamy, about2 minutes. Add eggs, one at a time, whisking until well combined after each addition. Whisk in vanilla.

Add flour mixture to sugar mixture alternately with buttermilk, beginning and ending with flour mixture, whisking just until combined after each addition. Spread batter into prepared pan.

Bake until a wooden pick inserted in center comes out clean, 50 to55 minutes. Let cool in pan for 10 minutes. Remove from pan, and let cool completely on a wire rack.

Spread Honey Buttercream onto cooled cake. Garnish with honey and peanuts, if desired. Refrigerate in an airtight container for up to 3 days.