Combine graham cracker crumbs, melted butter, brown sugar, and salt in a medium bowl. Stir until the mixture resembles wet sand and holds together when pressed.

Press the crumb mixture evenly into the bottom (and about 1/2 inch up the sides if you like) of the prepared springform pan using the bottom of a measuring cup or glass for firm compression.

Bake the crust for 8–10 minutes until fragrant and set. Remove from oven and let cool on a wire rack while you make the mousse.

Sweet Potato Mousse

If you do not have cooked sweet potato: Preheat oven to 400°F (200°C). Wash and pierce 2 medium sweet potatoes, wrap in foil, and roast 45–60 minutes until tender. Let cool, scoop flesh, and measure 2 cups mashed. (If using leftover or steamed sweet potato, ensure it's well-drained and smooth.)

In a small bowl, sprinkle gelatin over 3 tablespoons cold water and let bloom for 5 minutes. After it blooms, warm the gelatin gently (in 10–15 second bursts in the microwave or over a double boiler) until fully dissolved and fluid. Do not boil.

In a large mixing bowl, beat the softened cream cheese and softened butter together until smooth and no lumps remain, about 1–2 minutes with an electric mixer.

Add the mashed sweet potato, granulated sugar, vanilla extract, cinnamon, nutmeg, and maple syrup (if using) to the cream cheese mixture. Beat until fully combined and smooth. Taste and adjust sweetness or spices as desired.

With the mixer running on low, slowly pour the warm dissolved gelatin into the sweet potato mixture and continue to mix until incorporated and slightly thickened. This stabilizes the mousse so it sets in the refrigerator.

In a separate chilled bowl, whip 1 cup heavy cream to soft-medium peaks. To test: when you lift the whisk, peaks should hold briefly and then curl over. Fold one-third of the whipped cream into the sweet potato mixture to lighten it, then gently fold in the remaining whipped cream until uniform and airy. Do not overmix.

Pour the mousse evenly over the cooled graham cracker crust, smoothing the top with an offset spatula. Tap the pan gently on the counter to release air bubbles.

Cover the springform pan loosely with plastic wrap and refrigerate for at least 4 hours, preferably 6–8 hours or overnight, until the mousse is fully set.

Whipped Topping (Optional)

Chill a medium bowl and whisk (or mixer bowl and whisk) in the freezer for 10 minutes to help the cream whip faster.

Pour 1 cup heavy cream into the chilled bowl, add powdered sugar and 1/2 teaspoon vanilla. Whip at medium-high speed until medium-firm peaks form, about 2–3 minutes. Be careful not to overwhip into butter.

When the mousse cake has set, release the springform and transfer to a serving plate if desired. Dollop or pipe the whipped cream over the top. Optionally chill a few minutes more to set the decoration.

Garnish (Optional)

If using, toss chopped pecans with 1 tablespoon maple syrup and 1/4 teaspoon cinnamon. Spread on a parchment-lined sheet and toast in a 350°F (175°C) oven for 6–8 minutes until fragrant and lightly caramelized. Cool slightly.

Sprinkle the toasted pecans across the top of the cake or around the edge. Drizzle additional maple syrup if desired. Slice with a warm, dry knife (dip in hot water and wipe dry between cuts for clean slices).