Heat milk and heavy cream in a small pot until just before boiling.

Remove from heat.

Beat egg yolk and sugar until pale yellow.

Sift cornstarch or flour and add all at once to the egg mixture.

Slowly add rum and heated milk with heavy cream to the egg mixture.

Mix thoroughly.

Pass the mixture through a sieve.

Put the mixture back in the small pot.

Simmer over low-medium heat, mixing constantly with a spatula.

Cook until the mixture thickens and drips slowly from the spatula.

Turn off the heat immediately.

Pour into ramekins.

Sprinkle granulated sugar on top of each ramekin.

Heat a metal spoon in a gas flame until hot.

Place the hot spoon over the sugared top, moving it around until it sizzles.

Repeat until the sugar turns golden brown and forms a crispy top.

Chill before serving for a cold dessert.