Chocolate-Chestnut Mousse

Bring chestnuts, milk, sugar, vanilla, and salt to a boil over high heat in a small saucepan. Reduce heat, bring to a simmer, and cook, stirring occasionally, until milk is reduced by one-quarter and chestnuts smash fairly easily against the side of the pot with the back of a spoon, 15–17 minutes.

Meanwhile, finely chop 4 oz. chocolate. Using a peeler, shave remaining 1 oz. chocolate; set aside until ready to serve.

Purée chestnut mixture in a blender on high speed until very smooth, about 2 minutes. Add chopped chocolate and 1 tsp. brandy and blend on high speed until chocolate is melted, about 30 seconds. Scrape into a large bowl and let cool to room temperature, stirring occasionally (if lumps form, stir vigorously until smooth), 15–20 minutes.

Whip 2 cups cream with a whisk in another large bowl until it just barely holds soft peaks. Stir one-third of cream into chocolate mixture to lighten it, then fold in remaining cream just until incorporated. Transfer mousse to a large serving bowl, cover, and chill at least 2 hours or up to 1 day.

Whip remaining 1 cup cream and 1/2 tsp. brandy with whisk in a large bowl to medium peaks. Garnish mousse with reserved chocolate shavings and serve with whipped cream alongside.

Mousse can be made 1 day ahead; cover and chill.