Step 1

Heat the butter over medium heat in a saucepan until it foams.

Step 2

Stir in the mushrooms and season with salt.

Step 3

Simmer until the liquid evaporates, this will take about 20 minutes.

Step 4

Stir in the flour, cooking and stirring for about 5 minutes then add about 1 cup of beef stock, stirring briskly until incorporated, then pour in the remaining stock and mix thoroughly. Season with plenty of fresh cracked black pepper.

Step 5

Reduce heat to medium-low, and simmer until thickened, about 30 minutes, stirring often.

Step 6

Stir in fresh thyme leaves to taste, optional. Serve.