Pour the milk into a pan and whisk in the flour.
After the flour has combined into the milk, add in the lemon zest and cinnamon stick.
Bring the mixture to a simmer over a low heat, whisking continuously. Cook for about 2 to 3 minutes or until thick. It should be able to coat the back of a wooden spoon. Remove from heat.
Dissolve the sugar in 3/4 cup water in a smallpan over low heat.
Once the sugar is dissolved, increase the heat and boil until it reaches 223°F-234°F.
Gradually whisk the boiling sugar syrup into the milk mixture.
Place the egg yolks in a barge bowl. Pour the milk mixture over top while continuously whisking to combine.
Cover the surface with plastic wrap and leave to cool. Strain out the cinnamon stick and lemon zest before serving.
Enjoy!!