Place a sieve with a fine mesh over a big measuring cup or mixing bowl with a spout. Get six ramekins that hold 6 ounces.
Mix ½ cup (100g) sugar, cornstarch, and salt in a large basin. Add egg yolks and whisk until light and creamy, approximately 1 minute. A moist tea towel will keep the dish from slipping in the following stages.
Over medium-low heat, simmer milk, lemon zest, orange zest, and cinnamon in a heavy-bottomed pot. Mix the milk periodically to avoid burning.
Remove the pan from heat when the milk simmers. Remove zest and cinnamon stick with tongs. With one hand, steadily add hot milk into the yolk dish while whisking continually.
Pour the mixture back into the pot after adding all the milk. Stir frequently over medium-low heat until the custard thickens and simmers, approximately 5 minutes. After bubbling, cook for 1 minute while whisking.
Off the heat, pour the custard through the sieve into a large measuring cup or spout-equipped mixing basin. Pour custard into ramekins. Drape plastic wrap directly on the custard in each ramekin.
Sprinkle 2 tablespoons of the reserved ¼ cup (50g) sugar over each custard when ready to serve. Light your kitchen torch 4 inches over the sugar.
Circularly heat the sugar until it caramelizes to a deep brown.Serve quickly before caramel softens.