1. Preheat oven to 325°F (163°C). Spray a 9×13-inch cake pan with nonstick spray and line with parchment paper; spray parchment as well.
2. In a large bowl, whisk together flour, sugar, cocoa powder, baking soda, baking powder, and salt.
3. In another bowl, beat eggs lightly then add buttermilk, hot water, vegetable oil, and vanilla extract. Gradually combine wet and dry ingredients, mixing on low speed until smooth. Batter will be thin.
4. Pour batter into prepared pan and bake for 30-35 minutes until a toothpick comes out with moist crumbs. Cool completely in pan.
5. Poke holes evenly across the cooled cake using the back of a wooden spoon or a large straw.
6. Beat peanut butter briefly to loosen. Combine peanut butter with sweetened condensed milk and whole milk for glaze; stir until smooth. Pour glaze evenly over cake so it seeps into holes.
7. For whipped cream, beat peanut butter to soften. In a chilled bowl, whip heavy cream with powdered sugar and vanilla until stiff peaks form. Fold in peanut butter gently.
8. Spread peanut butter whipped cream over glazed cake.
9. Garnish with chopped peanut butter cups and peanuts if desired.
10. Refrigerate for several hours or overnight to set and meld flavors before serving.