1. Preheat oven to 350°F (176°C) and prepare a 9×13 inch cake pan with non-stick baking spray.
2. Add the flour, sugar, cocoa, baking soda, baking powder and salt to a large mixer bowl and combine. Set aside.
3. Add the milk, vegetable oil, vanilla extract and eggs to a medium sized bowl and combine.
4. Add the wet ingredients to the dry ingredients and beat until well combined.
5. Slowly add the hot water to the batter and mix on low speed until well combined. Scrape down the sides of the bowl as needed to make sure everything is well combined.
6. Pour the batter into the prepared cake pan and bake for 29-32 minutes, or until a toothpick comes out with a few moist crumbs.
7. Remove the cake from the oven. Using the end of a spatula, straw or something similar, poke holes all over the cake.
8. In a large measuring cup, combine the sweetened condensed milk and caramel sauce.
9. Pour the caramel mixture over the cake and spread it into the holes. Allow the cake to cool either in the fridge or at room temperature.
10. To make the whipped cream topping, add the heavy whipping cream, powdered sugar, peanut butter and vanilla extract to a large mixer bowl. Whip on high speed until stiff peaks form.
11. Spread the whipped cream on top of the cooled cake, then top with chopped Snickers and a drizzle of caramel and chocolate sauce.
12. Refrigerate cake until ready to serve. Cake is best for 3-4 days.