1 tablespoon flour
2 tablespoon butter
1 cup stock: chicken, fish etc…
1 cup cream
2 egg yolks
1 tablespoon lemon juice
salt and pepper, to taste
Melt butter in a small saucepan.
Add flour and stir 2 minutes over medium heat.
Add stock (fumet) stirring vigorously not to form lumps. ( Or half stock, half milk)
Let thicken over high heat for 1 minute.
Stir yolks into cream and add to sauce. Turn off heat at once.
Check seasoning and add lemon.
NOTE:
Fumet is the cooking liquid of the food you are making the sauce for.