If not already cooked, roast or boil one medium-large sweet potato until very tender (about 45 minutes roasted at 400°F / 200°C or 15–20 minutes boiled). Allow to cool, peel and mash until smooth. Measure 1 cup mashed sweet potato.

Bloom gelatin

Sprinkle 1 tsp unflavored gelatin over 2 tbsp cold water in a small bowl. Let stand 5 minutes to bloom.

Make sweet potato base

In a medium bowl, combine 1 cup mashed sweet potato, 3 tbs granulated sugar, 4 oz room-temperature cream cheese, 1 tbs softened butter, 1 tsp vanilla extract, 1 tsp ground cinnamon, 1 tsp ground nutmeg and a pinch of salt. Whisk or beat with a hand mixer until smooth and uniform.

Dissolve gelatin

Microwave the bloomed gelatin for 10–15 seconds or warm it in a small saucepan over low heat until dissolved (do not boil). Immediately whisk the dissolved gelatin into the sweet potato mixture to incorporate evenly.

Whip cream and fold

In a separate chilled bowl, whip 1 cup heavy cream to soft-medium peaks. Fold one-third of the whipped cream into the sweet potato mixture to lighten it, then gently fold in the remaining whipped cream until uniformly combined. Chill the mousse in the refrigerator for at least 30 minutes to set slightly while you prepare the cake layers.

Cake Layers (Sponge / Butter Cake)

Preheat and prepare pan

Preheat oven to 350°F (175°C). Butter and line an 8x8-inch pan (or prepare two 6-inch round pans) with parchment, or use nonstick spray. This recipe is scaled for an 8x8-inch single-layer that will be sliced into pieces; you may split batter for two thin layers if desired.

Mix dry ingredients

In a small bowl, whisk together 1 cup all-purpose flour, 1 tsp baking powder and a pinch of salt until evenly combined.

Whisk eggs and sugar

In a medium bowl, whisk 2 large eggs with 3 tbs granulated sugar and 1 tsp vanilla until pale and slightly thickened, about 1–2 minutes by hand or 1 minute with an electric mixer.

Combine wet and dry

Add 1 tbsp milk and 3 tbsp melted butter to the egg mixture and whisk briefly to combine. Sift or fold the dry ingredients into the wet mixture gently until no streaks remain—do not overmix to keep the cake light.

Bake

Pour batter into the prepared pan and smooth the top. Bake in the preheated oven for 12–18 minutes (thin layer) or 20–25 minutes (thicker 8x8) until the top is golden and a toothpick inserted in the center comes out clean. Remove from oven and let cool in pan for 10 minutes, then transfer to a wire rack to cool completely. If you made two layers, level them as needed.

Slice to pieces

Once the cake is completely cool, slice into desired serving pieces (for example, eight small rectangles or squares). If you made round layers, cut each round into wedges or assemble mousse between two thin rounds.

Assembly & Garnish

Assemble mousse piece cakes

Place a slice of cake on a serving plate. Pipe or spoon a generous layer (about 2–3 tbs) of chilled sweet potato mousse over the cake slice. If making multiple layers, spread mousse between cake layers and top with an additional thin layer of mousse for a neat finish.

Chill to set

Refrigerate assembled pieces for at least 30–60 minutes to allow the mousse to set properly and the flavors to meld. Chilling also makes slicing and serving cleaner.

Garnish and serve

Before serving, dust with 1 tsp powdered sugar and sprinkle with 2 tbs chopped toasted pecans or walnuts, if using. Serve chilled or slightly chilled. Store leftovers covered in the refrigerator for up to 3 days.