Sweet PotatoPraline Spice Cake with Marshmallow Meringue
For this spectacular cake, I took the iconic marshmallow-topped sweet potato casserole and turned it into a glorious towering dessert: six layers of spicy sweet potato cake sandwiched with a rich, buttery praline filling and swathed in a glossy cloud of burnished marshmallow meringue. I like to use garnet yams (which are, in fact, sweet potatoes and not yams, just to confuse you). Their bright orange flesh is dense, moist, and subtly sweet. This cake is particularly fun to serve after Thanksgiving dinner. You can make the cake layers and freeze them up to 2 weeks ahead of time. Fill and frost the cake the morning of the big event.
- 3 cups [420 g] all-purpose flour
- 2 tsp baking powder
- 1 tsp baking soda
- 11/4 tsp fine sea salt
- 4 tsp ground cinnamon
- 1 tsp ground ginger
- 1 tsp ground allspice
- 1/2 tsp freshly grated nutmeg
- 1/2 tsp ground cloves
- 2 medium sweet potatoes such as garnet yams
- 4 eggs
- 11/2 cups [300 g] firmly packed dark brown sugar
- 1 cup [200 g] granulated sugar
- 3/4 cup [180 ml] buttermilk
- 1/2 cup plus 2 Tbsp [140 g] unsalted butter, melted
- 1/2 cup [120 ml] canola or vegetable oil
- 3 Tbsp bourbon, dark rum, or cognac
- 2 tsp vanilla extract
BROWN BUTTER-PRALINE FILLING
- 1 cup [220 g] unsalted butter, at room
- 2 cups [400 g] firmly packed dark brown sugar
- 2 Tbsp Golden Syrup or dark corn syrup
- 11/3 cups [320 ml] heavy cream
- 2 Tbsp bourbon, dark rum, or Cognac
- 1/2 teaspoon fine sea salt
- 3 cups [360 g] confectioners’ sugar, sifted
- 11/2 tsp vanilla extract
- 3 egg whites
- 11/2 cups [300 g] granulated sugar
- 1/2 cup [170 ml] light corn syrup
- 1/4 cup [60 ml] water
- 11/2 tsp vanilla extract
Position a rack in the center of the oven. Preheat the oven to 375°F [190° C]. Coat three 8-in [20-cm] round cake pans with nonstick cooking spray and line the bottoms with parchment paper.
Sift together the flour, baking powder, baking soda, salt, cinnamon, ginger, allspice, nutmeg, and cloves into a medium bowl. Set aside.
Prick the sweet potatoes all over with a fork and bake on a rimmed baking sheet until they are very tender when pierced with a knife, about 1 hour. Remove from the oven and let cool completely. Halve the potatoes, scoop the flesh into a bowl, and mash with a fork. Measure 2 packed cups [460 g] of the flesh into a food processor fitted with the metal blade and pulse until smooth.
Add the eggs and sugars to the food processor and pulse to combine. Pour the buttermilk, melted butter, oil, bourbon, and vanilla through the feeding tube, processing with a few short pulses, just until smooth.
Remove the top of the processor and scrape down the sides. Add the dry ingredients and give the processor a few final pulses until the batter is smooth. Divide the batter evenly between the prepared pans and smooth the tops with a spatula. Tap the pans once or twice on the counter to settle the batter.
Bake for 30 to 35 minutes, until a wooden skewer inserted into the center of each cake comes out with just a few moist crumbs clinging to it. Let the cake layers cool in their pans on wire racks for 10 minutes, and then invert them onto the racks. Discard the parchment paper. Let cool completely before frosting.
To make the Brown Butter-Praline filling:
Melt 3/4 cup [170 g] of the butter in a medium saucepan over low heat. When the butter is melted, increase the heat to medium-high and bring to a boil, stirring constantly. As the butter boils, it will snap and sizzle and sound like distant applause or frying bacon. As the water in the butter burns off, the sizzling will slowly die down, and that is when the milk solids in the butter will start to brown and develop a sweet and nutty aroma. Stir constantly, scraping up the browned bits on the bottom of the pan, and to ensure the butter browns evenly, 3 to 5 minutes.
Remove from the heat and immediately stir in the brown sugar, golden syrup, bourbon, and cream. Return the pan to the heat and cook, stirring occasionally, until the sugar dissolves. Bring to a boil and cook for exactly 2 minutes. (Set a timer!) Remove from the heat and scrape into the bowl of a stand mixer fitted with the paddle attachment. With the mixer on low speed, beat in the sifted confectioners’ sugar. Continue beating until the frosting is thick and creamy and the mixer bowl is cool to the touch, 5 to 6 minues. Beat in the remaining 4 Tbsp [60 g] room temperature butter, 1 Tbsp at a time, until fully incorporated.
With a long, serrated bread knife, cut each cake layer in half horizontally (see page 21). Place one layer, cut-side up, on a cake plate or cake stand. Spread one-fifth of the praline filling over the top of the cake, pushing it to the edges. Top with a second layer, cut-side down. Continue frosting and stacking the remaining cake layers. Top with the final layer of cake, cut-side down.
to make the Marshmallow Meringue:
In a stand mixer fitted with the whisk attachment, beat the egg whites on medium speed until soft peaks form, 3 to 4 minutes.
In a 3-qt [3-L] saucepan, stir the sugar, corn syrup, and water together until well blended. Over medium heat, bring to a rolling boil, covered. Uncover and boil 4 to 8 minutes, without stirring, until the syrup reaches 242°F [116°C] on an instantread candy thermometer (tip the pan to one side so the syrup is deep enough for the thermometer to accurately measure the temperature), or until 1/2 tsp of the syrup dropped into cup of ice water forms a soft, malleable ball (see page 91). With the mixer on medium speed, slowly pour the hot syrup in a thin, steady stream into egg whites, beating constantly. Add the vanilla. Increase the mixer speed to high and continue beating for 8 to 10 minutes, until the meringue is stiff and glossy, but still warm.
Using a rubber or silicone spatula, scrape all the meringue onto the top of the cake. With an offset spatula, quickly spread the marshmallow meringue thickly over the top and sides of the cake. Use the spatula or the back of a spoon to create swirls and spikes all over the cake. At this point, the cake can sit at room temperature up to 8 hours before browning the meringue.
To finish the cake:
Right before serving, use a propane blowtorch or butane kitchen torch to lightly brown the meringue: Hold the torch 2 to 3 inches from the cake, waving the flame over the meringue to caramelize it lightly. Serve immediately, slicing the cake into thin wedges with a long, thin knife. Any leftovers can be stored in a covered cake carrier at room temperature for 1 more day.