In a saucepan, heat the milk with lemon zest, orange zest, and cinnamon stick on medium until it simmers. Then remove from heat.

Make a slurry by mixing cornstarch with a bit of water.

Whisk egg yolks and sugar until pale, then mix in the cornstarch slurry and some hot milk.

Take out the zest and cinnamon from the milk, and gradually add the egg mix, whisking to avoid curdling.

On low heat, stir constantly until the mix thickens like pudding.

Pour into ramekins, cover with plastic wrap directly on the custard, and chill for 4 hours or overnight.

Before serving, remove wrap, add a sugar layer on each custard, and caramelize with a torch or broiler.

Serve immediately, optionally with fresh fruit on top.