Preheat your oven to 350°F (175°C) and grease the baking dish. Combine the cake mix and its ingredients, adding vanilla if using. Mix well and set aside.

Pour the batter into the baking dish. Bake for 25-30 minutes until a toothpick comes out clean.

Let the cake cool for about 10 minutes, then poke holes across the surface using a wooden spoon handle.

Whisk together peanut butter, sweetened condensed milk, and whole milk until smooth. Pour over the warm cake, allowing it to seep into the holes.

Beat the heavy cream and powdered sugar until soft peaks form, then add peanut butter and mix until fluffy.

Spread the whipped topping over the cooled cake and garnish with crushed Reese’s cups and peanuts. Drizzle with melted chocolate and peanut butter if desired.

Cover and refrigerate for at least 1 hour before serving.