Get ready: Set a fine mesh sieve over a large measuring cup or spouted mixing bowl. Gather six 6-ounce ramekins.

Whisk the eggs: In a large bowl, whisk together ½ cup (100g) of the sugar, the cornstarch, and salt. Add the egg yolks and whisk until the mixture becomes pale and smooth, about 1 minute. Set the bowl on a damp tea towel to prevent it from sliding in the next steps.

Infuse the milk: In a medium, heavy-bottomed saucepan, bring the milk, lemon zest, orange zest, and cinnamon to a simmer over medium-low heat. Stir the milk occasionally to prevent it from scorching.

Temper the egg mixture: As soon as the milk reaches a simmer, take the pan off the heat. Use tongs to remove the zest and cinnamon stick. With one hand, slowly pour the hot milk into the bowl of yolks, whisking constantly with your other hand.

Whisk and simmer: Once all of the milk has been incorporated, pour the mixture back into the saucepan. Cook over medium-low heat, whisking constantly until the custard thickens and comes to a simmer, about 5 minutes. Once it begins to bubble, continue cooking, still whisking, for 1 minute.

Strain, pour, and chill: Take the custard off the heat and pour it through the sieve into the large measuring cup or mixing bowl with a spout. Pour the custard into the ramekins. Cover each ramekin with plastic wrap, draping the plastic directly on the surface of the custard. Chill in the refrigerator overnight, or at least 4 hours. The custards will keep in the fridge for up to 4 days.

Ignite!: When you’re ready to serve, use the reserved ¼ cup (50g) sugar to sprinkle over the top of each custard, about 2 teaspoons of sugar per custard. Ignite your kitchen torch and hold the flame about 4 inches above the layer of sugar. Move the flame in circles until the sugar melts and caramelizes to a deep brown.

Serve: Serve immediately, before the caramel softens.