Preheat oven to 350°F. Spray a bundt pan with nonstick cooking spray (I like using the kind with flour in it).

Whisk together cake mix and pudding mix in a large bowl. Add eggs, melted butter, milk, and extract if using. Whisk until mostly smooth.

Pour batter into prepared pan. Bake for 30-40 minutes, or until a toothpick comes out mostly clean from the center of the cake.

As soon as the cake comes out of the oven, make the sauce: melt butter in a small saucepan over medium heat. Add the sugar, cocoa, and water. Stir and bring to a boil, cooking until the sugar is dissolved and the sauce is no longer grainy, about 2-3 minutes. Remove from heat and stir in vanilla.

Even though the cake is still hot, we’re going to remove it from the pan. Invert the cake onto a rack set over a cookie sheet.

Using a long skewer, poke several small holes all over the cake. Carefully pour hot chocolate butter sauce over the cake, allowing any extra to drip onto the cookie sheet under the rack. (If you want, you can scoop this extra sauce up off the pan and drizzle it over the cake again.)

Let the cake cool then transfer to a serving plate. Store loosely covered for up to 3 days.