Combine the cream and vanilla in a saucepan over low heat; bring to a light simmer, then turn off the heat and infuse for 10 minutes.
In a separate bowl, whisk the egg yolk with 3 tbsp of sugar until smooth.
Slowly pour the warm cream into the egg mixture while whisking continuously to temper the yolks.
Pour the custard into a ramekin and place it in a larger baking dish filled halfway with boiling water (bain-marie).
Bake at 160°C for 25–28 minutes until the edges are set but the center is still jiggly.
Cool to room temperature, cover with cling film, and refrigerate for 4–6 hours to set completely.
Sprinkle the remaining 1 tbsp of sugar evenly over the cold custard.
Heat a metal spoon over the stove until red hot, then press and move it over the sugar to caramelize into a crisp shell.