Preheat the oven to 120C/250F/Gas ½.
For the crème brûlées, place the egg yolks into a bowl, add the caster sugar and vanilla and whisk together until pale and fluffy and well combined.
Add the milk and cream and whisk until well combined.
Ladle the mixture into ramekins and place the ramekins into a deep roasting tin.
Place the tin into the oven and pour in enough boiling water to come halfway up the sides of the ramekins. Bake for one hour, or until just set.
Remove from the roasting tin and allow to cool. When cool, refrigerate the crème brûlées for at least two hours, or until thoroughly chilled and firm.
For the strawberry sauce, place half of the strawberries into a food processor and blend to a purée. Strain through a fine sieve.
Halve the rest of the strawberries and stir through the passed sauce.
When ready to eat, sprinkle the demerara sugar over the top of the brûlées and caramelise with either a chef’s blowtorch or by putting them under a hot grill until the sugar starts to bubble and caramelised. Place each dish on a plate and serve with the strawberry sauce in a small dish alongside.