another recipe is milk, cream, butter, and flour. In a double boiler add milk and cream together. You can add a whole onion and a few bay leaves to add a little flavour to it. let it simmer till the onion becomes soft. Mix raw butter and flour in a bowl till it resembles shortbread cookie dough. Use this mixture to thicken the sause. Remove the onion and bay leaves the pour the sause through a strainer and it's ready to use.