Combine the cornstarch, cocoa, and sugar in a small heavy-bottomed saucepan.

With the pan on low heat, slowly pour in the cold milk, whisking to combine.

Increase the heat to medium-high and continue whisking (to prevent any lumps) until the mixture boils, about 1 minute. Remove the pan from the heat and stir in the vanilla.

Let cool in the refrigerator with plastic wrap on the surface to prevent a skin from forming. Serve in individual cups, ramekins, or glasses. Garnish with candied hazelnuts, if desired.

For Candied Hazelnuts:

Lay a piece of aluminum foil on your work surface.

Melt the brown sugar in a saucepan over low heat. Add the nuts and bring the mixture to a boil without stirring. When the sugar starts to deepen in color and a candy thermometer reads 236°F, pour the mixture onto the foil and let it cool completely.

Break the hardened hazelnut brittle into pieces and sprinkle them on top of puddings, cakes, or cupcakes, for a little added crunch.

Mexican-chocolate pudding:

Add ½ teaspoon ground organic cinnamon and a pinch of cayenne pepper to the dry ingredients. Top the pudding with a dollop of whipped cream and a sprinkling of black sea salt.