Autumn Delight Cake
Sweet Potato & Ginger Layer Cake with Toasted Marshmallow Filling, Candied Pecans and Brown Sugar & Cinnamon Buttercream
For the Cake Layers:
  • 3 large sweet potatoes about 900 g
  • 2 cups 400 g sugar
  • 4 large eggs at room temperature
  • 1-1/4 cups 315 ml sunflower oil (or vegetable, safflower, canola oil)
  • 2 cups 230 g cake flour
  • 1 tablespoon 7 g ground cinnamon
  • 2 teaspoons 8 g baking powder
  • 1 teaspoon 7 g salt
  • 1 teaspoon 3 g ground nutmeg
  • 1/2 teaspoon 1.5 g ground ginger
  • 2 tablespoons 30 ml brandy or dark rum
  • 2 teaspoons 10 ml pure vanilla extract
  • 3/4 cup 120 g crystallized ginger, chopped
For the Filling:
  • 16 large white marshmallows
  • 1 cup 125 g icing sugar (confectioners' or powdered), sifted
  • 1 cup butter 227 g(2 sticks), at room temperature
  • 1/2 teaspoon 2.5 mL pure vanilla extract
  • 1 jar 213 g marshmallow cream (such as Marshmallow Fluff)
For the Buttercream:
  • 5 large egg whites 150 g)
  • 1-1/4 cups 250 g light brown sugar
  • 1-1/2 cups 3 sticks(340 g) unsalted butter, softened and cut into cubes
  • 2 teaspoons 10 ml pure vanilla extract
  • pinch of salt
  • a few pinches of cinnamon to taste
For the Candied Pecans:
  • 2 tablespoons 28 g unsalted butter
  • 2 tablespoons 24 g brown sugar
  • 1 cup 100 g pecan pieces
For the Cake Layers:
  1. Preheat oven to 350°F. Grease two 8-inch round cake pans, dust with flour, tap out excess and set aside.
  2. Place the sweet potatoes on a microwave-safe plate and pierce them with a fork. Microwave until they are tender (about 7-8 minutes each side). Carefully remove the skin when cool enough to touch, and mash the flesh into a coarse puree.
  3. In the bowl of an electric mixer fitted with the paddle attachment, beat the sugar and eggs together on medium-high speed (I use #6 on KitchenAid) until light and fluffy, about 5 minutes. Add the oil and beat on medium until combined. Add the cooled sweet potato puree and mix until combined.
  4. Sift dry ingredients together (cake flour, cinnamon, baking powder, salt, nutmeg and ground ginger) and then add to sweet potato mixture.
  5. Mix in brandy/dark rum (I used dark rum) and vanilla. Gently stir in crystallized ginger.
  6. Evenly distribute batter into the prepared pans (weigh them if possible with digital kitchen scale), smooth with a small offset palette knife and place in the center of the middle rack of the oven, about 2 inches apart. Bake until a knife or skewer inserted into the center comes out clean, about 40 minutes.
  7. Let pans cool on a wire rack 10 minutes. Invert cakes onto rack and cool them completely.
For the Filling:
  1. Place marshmallows on cookie sheet lined with parchment paper and sprayed with nonstick cooking spray. Place on lower rack of oven, and broil marshmallows until nice and brown on top, between 30-60 seconds. Remove pan from oven and gently turn the marshmallows over, and broil until they are golden brown. (Be sure to keep an eye on them--they burn very quickly.)
  2. In an electric mixer fitted with paddle attachment, combine butter and icing sugar on low until blended, about 1 minute. Add vanilla and mix on med-high for about 3 minutes.
  3. Add marshmallow cream and toasted marshmallows, and mix on lowest setting for about 1 minute.
For the Buttercream:
  1. Wipe the bowl of an electric mixer with paper towel and lemon juice, to remove any trace of grease. Add egg whites and sugar, and simmer over a pot of water (not boiling), whisking constantly but gently, until temperature reaches 160°F, or if you don't have a candy thermometer, until the sugar has completely dissolved and the egg whites are hot.
  2. With whisk attachment of mixer, begin to whip until the meringue is thick, glossy, and the bottom of the bowl feels neutral to the touch (this can take up to 10 minutes or so). *Don't begin adding butter until the bottom of the bowl feels neutral, and not warm.
  3. Switch over to paddle attachment and, with mixer on low speed, add butter cubes, one at a time, until incorporated, and mix until it has reached a silky smooth texture (if curdles, keep mixing and it will come back to smooth). *If mixture is too runny, refrigerate for about 15 minutes and continue mixing with paddle attachment until it comes together. Add vanilla and salt, continuing to beat on low speed until well combined. Add cinnamon to taste and blend.
For the Candied Pecans:
  1. Melt the butter in a small pan. Mix in brown sugar, and add the pecans. Toss to coat.
  2. Cook on medium low heat for about 15 minutes, stirring occasionally. Be sure to watch carefully so they don’t burn.
  3. Turn out onto parchment paper or aluminum foil and let cool for 5 minutes; break apart into smaller pieces if using halves.
Assembly of the Autumn Delight Cake
  1. Slice both cake layers in half horizontally, so you have 4 cake layers.
  2. Place the first layer on a plate, pedestal or cake board cut side up (so bottom of the cake layer is touching plate), and spread ~3/4 cup of Toasted Marshmallow Filling with a small offset palette knife, leaving 1" or so around the edge. Sprinkle with a handful of candied pecans pieces.
  3. Repeat previous step until you get to the final cake layer. Place last layer face down and chill cake for 30-40 minutes.
  4. Frost cake with Brown Sugar Buttercream and top with a generous handful of candied pecans and crystallized ginger.
  5. Finished cake can be kept at room temperature for up to 8 hours. Keep refrigerated if longer than 8 hours, but always serve at room temperature (Swiss Buttercream should never be served cold, as it goes back to a cold-butter texture).
Sweetapolita's Notes

* You can make buttercream ahead and keep in an airtight container in refrigerator for up to one week, leaving out at room temperature when needed, re-whipping in mixer for 5 minutes.

**Can freeze buttercream for up to 6-8 weeks. To thaw, place on counter overnight, and rewhip for 5 minutes with paddle attachment in an electric mixer. If not satiny enough upon rewhip, take 1/3 of buttercream and microwave in a microwave-safe container for ~8 seconds, then add back to mixing bowl and remix with remaining buttercream.