Heat oven to 150 C / 300 F. Place six 150 ml ramekins inside a deep roasting pan.

Add 150 g sugar and 2 tbsp water to a heavy-bottomed saucepan over medium heat. Swirl the pan gently as the sugar dissolves but do not stir.

Increase heat to medium-high and cook without stirring until the caramel turns a deep amber, almost mahogany color, about 8 to 10 minutes. Watch carefully from 6 minutes onward.

Remove from heat immediately. Carefully pour in the 400 ml heavy cream in a slow, steady stream, it will bubble violently. Whisk until smooth. If the caramel seizes into lumps, return to low heat and stir until dissolved.

Add the 150 ml whole milk and stir to combine. Set aside to cool for 5 minutes.

In a large bowl, whisk together 6 egg yolks, 30 g sugar, 1 tsp vanilla extract, and a pinch of fine sea salt until the mixture is pale and slightly thickened, about 2 minutes.

Slowly pour the warm caramel cream into the egg yolk mixture in a thin stream, whisking constantly to temper the eggs and prevent scrambling.

Strain the entire mixture through a fine-mesh sieve into a large jug for easy pouring. Discard any solids.

Divide the custard evenly among the six ramekins, filling each to about 1 cm from the top.

Pour hot water into the roasting pan until it reaches halfway up the sides of the ramekins.

Bake at 150 C / 300 F for 40 to 50 minutes until the edges are set and the center has a 2-inch wobble when the pan is gently shaken. An instant-read thermometer should read 77 C / 170 F at the center.

Remove ramekins from the water bath and let cool to room temperature on a wire rack, about 30 minutes.

Cover each ramekin with plastic wrap and refrigerate for at least 3 hours, or overnight, before serving.