Add <quantity>125<unit>ml</unit></quantity> of milk and <quantity>125<unit>ml</unit></quantity> of cream to a saucepan

Add <quantity>100<unit>g</unit></quantity> of egg yolk and whisk to combine. Turn the heat on to low

Add <quantity>200<unit>g</unit></quantity> of diced gruyère cheese and stir until it starts to melt

Keep stirring until the mixture reaches <temperature>82<unit>°C</unit></temperature>. Turn off the heat

Transfer the mixture to a tall container and blend with a hand blender on low speed until smooth

Cover with plastic wrap and refrigerate until completely chilled and firm

Add <quantity>500<unit>g</unit></quantity> of cold cream cheese and the chilled cheese mixture to a bowl. Mix with a spatula until thoroughly combined

Transfer to a piping bag. Tie it and trim off the excess from the top of the bag. The cheese custard is ready

Enjoy! This is great to fill gougères or to add to a sandwich!