Step 1

Preheat the oven to 350°F and grease a 9x13-inch metal cake pan (don’t use glass; metal pans provide straighter sides). Line the bottom of the pan with parchment paper and spray lightly with nonstick spray. Set aside.

Step 2

Place all the cake ingredients (except for the ice cream) in a large bowl. Mix with an electric hand mixer on low speed for about 30 seconds. Scrape the bowl. Then mix on medium speed for 2 minutes, scraping the bowl as necessary.

Step 3

Pour the batter into the prepared pan and smooth the surface with a spoon or spatula. Bake for 22 to 25 minutes, until the cake starts to shrink away from the sides of the pan and springs back when pressed lightly.

Step 4

Place the pan on a wire rack to cool for 10 minutes. Then remove the cake from the pan, peel off the parchment paper, and place the cake on the wire rack to cool completely.

Step 5

Combine all the sauce ingredients (except for the vanilla) in a heavy-bottomed saucepan over medium heat, stirring constantly until all the chocolate has melted.

Step 6

Remove the pan from the heat and stir in the vanilla. Keep warm or reheat before serving.

Step 7

If the top of the cake is uneven, level it with a knife. Carefully slice the cake in half horizontally, creating two thinner layers of cake, each about 3/4 inch thick. Leave the layers in place and cut the cake in half along its width to create 4 rectangles, each about 9 x 6 inches. Set half of the cake aside (for another use or to make a second hot fudge cake).

Step 8

Place 2 layers of plastic wrap on the counter, large enough to wrap the assembled ice cream cake. Place one rectangle of cake onto the wrap.

Step 9

Peel off the cardboard from around the ice cream and slice the ice cream into 3/4-inch slices. Arrange the slices on top of the cake so that the surface of the cake is completely covered.

Step 10

Trim the ice cream to match the dimensions of the cake and put any leftover ice cream in a freezer container to eat later.

Step 11

Place the second rectangle of cake on top of the ice cream and press down lightly.

Step 12

Wrap the cake with the plastic wrap and freeze for at least 2 hours.

Step 13

Slice the cake into 6 squares and place each square on a serving plate.

Step 14

Pour some of the hot fudge sauce over each square and top with whipped cream and a cherry.