Mix egg yolks and sugar in a small bowl until well combined.

Combine milk and vanilla bean paste in a saucepan and stir.

Heat the mixture gently until the edges start to bubble, then remove from heat.

Gradually pour the milk mixture into the egg yolk mixture while stirring constantly.

Return the mixture to the saucepan.

Cook over low heat, stirring continuously, until thickened.

Remove from heat when the mixture reaches about 80°C and leaves a trail when you scrape the pan bottom.

Strain the custard through a sieve and cool it over an ice bath.

Gradually mix the butter into the cooled custard cream in batches.