Preheat oven to 350°. Spray a 13x9-inch metal baking pan with baking spray with flour.
In a large bowl, stir together brown sugar, peanut butter, and oil until combined and creamy. Add eggs and vanilla, stirring just until combined.
In a medium bowl, sift together flour, baking powder, baking soda, and salt. Gradually add flour mixture to sugar mixture alternately with buttermilk, beginning and ending with flour mixture, stirring just until combined after each addition. Pour batter into prepared pan.
Bake until a wooden pick inserted in center comes out clean, 35 to 40 minutes. Let cool in pan completely. Using a skewer, poke cake all over. Reserve 3 tablespoons Cola Syrup. Using a pastry brush, brush all remaining Cola Syrup over cake. Top with Peanut Butter Cream Cheese Frosting. Garnish with peanuts and serve with reserved syrup, if desired.
Cola Syrup
In a medium saucepan, heat cola over medium heat. Let simmer, stirring occasionally, until reduced to ¾ cup and slightly thickened, about 1 hour, adjusting heat if needed. Pour into bowl and let cool to room temperature.
Peanut Butter-Cream Cheese Frosting
In the bowl of a stand mixer, beat butter and cream cheese on low until creamy. Add peanut butter and vanilla, beating until combined. Gradually add confectioners’ sugar, beating until smooth. Increase speed to medium, beating until fluffy, 1 to 2 minutes. Use immediately.
Notes
The Cola Syrup can be made ahead of time and refrigerated in an airtight container for up to 1 week. Simply set out to warm at room temperature, or microwave for 10 to 15 seconds or just until easily brushable and no longer cool to the touch.
Recipe by Taste of the South at https://tasteofthesouthmagazine.com/peanuts-cola-poke-cake/