Preheat oven to 350°F. Line a 9-inch square baking pan, with high sides, with parchment paper and grease lightly with cooking spray. Set aside.

In a large bowl, whisk together the flour, sugar, baking soda, baking powder, and salt. Set aside. In a separate bowl, whisk together the buttermilk, eggs, and vanilla and add to the dry ingredients, stirring until just combined.

In a medium saucepan, combine the water, butter and peanut butter and set over moderate heat. Cook, stirring often, until melted through and smooth. Remove from heat and allow to cool. Add to the batter and whisk until smooth and well combined. Transfer the batter to the prepared pan and give it a few taps on the counter to remove any air bubbles. Bake until golden brown and a toothpick, inserted in the middle, comes out clean, about 30 to 35 minutes. Remove from the oven and allow to cool for 10 minutes in the pan. Use the parchment paper to lift the cake from the pan. Set on a wire rack to cool completely.

To make the ganache, warm the heavy cream either on the stove in a saucepan or in a glass measuring cup in the microwave. Pour over the chocolate and allow to sit for 5 minutes before stirring until smooth and glossy. Pour the ganache over the top of the cake and spread out slightly.

To make the meringue, beat the egg whites, cream of tartar, vanilla and salt on high until soft peaks form. While mixer is running on low, slowly add the sugar in a slow steady stream. Beat on high until glossy stiff peaks form. Dollop the meringue onto the cake and create swirls with the back of a spoon or spatula. Toast the top of the meringue with a kitchen torch. Slice and serve immediately or store in the fridge until ready to eat. Enjoy!