Dark Chocolate Pudding

large egg, plus 2 yolks

ounces/170 grams bittersweet chocolate, preferably 66 percent to 74 percent cacao, chopped

tablespoons/30 grams unsalted butter, softened

teaspoon/5 milliliters vanilla extract

cups/590 milliliters whole milk

cup/120 milliliters heavy cream

cup/67 grams light or dark brown sugar

tablespoons/15 grams unsweetened cocoa powder

tablespoons/20 grams cornstarch

teaspoon/2 grams fine sea salt

Whipped cream or crème fraîche, for serving

Chocolate shavings, for garnish (optional)

Flaky sea salt, for garnish (optional)