Preheat oven to 350°F (175°C). Grease and line two 6-inch round cake pans (or one 9x5 loaf pan if making a single-piece cake). Whisk together all-purpose flour, baking powder and 1/2 tsp salt in a bowl and set aside. In a separate large bowl, cream 1/2 cup unsalted butter and 3/4 cup granulated sugar until light and fluffy (about 3–4 minutes). Add eggs one at a time, beating well after each addition. Stir in 1 tsp vanilla extract. Fold in 1/2 cup almond flour. Alternately add the dry flour mixture and 1/2 cup milk, beginning and ending with the dry ingredients; mix until just combined. Divide batter evenly between prepared pans and smooth tops. Bake until a toothpick inserted into the center comes out clean, about 20–25 minutes for 6-inch pans (35–40 minutes for a 9x5 loaf). Cool in pans 10 minutes, then turn out to a wire rack and cool completely.

Sweet Potato Mousse

Bloom gelatin

Place 3 tablespoons cold water in a small bowl and sprinkle 1 tablespoon unflavored gelatin over the surface. Let sit 5–7 minutes until gelatin blooms and becomes spongy.

Prepare sweet potato base

In a medium saucepan over low heat, combine 2 cups mashed cooked sweet potato, 1 cup granulated sugar, 1 tsp ground cinnamon, 1 tsp ground nutmeg and a pinch of salt. Stir to combine and warm gently until sugar is dissolved and mixture is smooth, about 3–4 minutes. Remove from heat. Taste and adjust sweetness if desired.

Incorporate gelatin

Microwave the bloomed gelatin for 10–15 seconds or warm it over a double boiler just until it liquefies (do not boil). Stir 1–2 tablespoons of the warm sweet potato mixture into the gelatin to temper, then pour the gelatin mixture back into the saucepan with the sweet potato and whisk until fully incorporated and smooth. Allow to cool slightly (5 minutes) but not set.

Whip cream

In a chilled bowl, whip 1 cup heavy cream with 2 tablespoons powdered sugar and 1 teaspoon vanilla extract to soft-medium peaks (not too stiff).

Fold and chill

Fold one-third of the whipped cream into the slightly cooled sweet potato mixture to lighten it, then gently fold in the remaining whipped cream until fully combined and airy. Taste and adjust spices or sweetness. Transfer the mousse to the refrigerator to chill for at least 30–45 minutes until slightly firm but still pipeable.

Assembly & Garnish

Level and optionally glaze cake layers

If cake tops domed, level them with a serrated knife. If desired, brush each cake surface lightly with 1 tablespoon warmed apricot jam to add shine and trap crumbs.

Layer the cake

Place one cake layer on your serving board or plate. Pipe or spread about half of the sweet potato mousse evenly over the layer, smoothing to the edge. Top with the second cake layer and spread the remaining mousse over the top and sides, or leave the sides naked for a 'piece cake' look and just top with mousse. Use an offset spatula to smooth edges.

Chill to set

Refrigerate the assembled cake for at least 1 hour (preferably 2–3 hours) to allow mousse to set and flavors to meld.

Garnish and serve

Before serving, garnish the top with toasted chopped pecans or almonds, candied orange slices or zest, and a light dusting of powdered sugar. Slice with a sharp knife wiped clean between cuts. Serve chilled or at cool room temperature. Leftovers keep refrigerated for up to 3 days.