Melt the butter in a medium saucepan. Add the flour.

Whisk together the butter and flour and cook for a minute over medium heat until it is smooth.

Whisk in the chicken stock. Let the mixture come to a bubble. The roux will not thicken until it comes to a bubble. Cook for another minute or so after it comes to a bubble.

Add the brandy and thyme.

Season well with salt and pepper. Put this in a container and keep in the fridge. When you are ready to serve it, simmer it in a saucepan until it is heated through.