Sweet potatoes

Wrap the sweet potatoes in aluminum foil and bake in an oven at 180-200°C for about an hour until they are soft enough that you can easily pierce them with a bamboo skewer

Cut the sweet potato in half lengthwise, then in half top to bottom, and then cut into quarters

Peel off the fruit with a spoon, being careful not to break the skin, and strain through a fine sieve

Transfer [3] to a saucepan, add the milk, heavy cream, half of the granulated sugar, and butter, and beat over high heat. If you add the granulated sugar all at once, it will harden, so it's best to add it in several batches

After kneading for about 5 minutes, turn off the heat, add 1 egg yolk and mix well. Add vanilla extract, the remaining granulated sugar and 1 more egg yolk and mix until smooth

Place the reserved sweet potato skins from step [3] into a sweet potato mold, and use a palette knife to arrange the filling from step [5]. After smoothing the surface, brush with beaten egg yolk for finishing

Place in an oven preheated to 180°C and bake on the middle rack for about 10 minutes. To ensure even browning, switch the baking tray over halfway through and bake for an additional 2 minutes. Garnish with fresh cream and chervil leaves to finish, if desired