Wash and drain the mushrooms.  I purchase whole mushrooms and slice them myself, but you can also purchase pre-sliced mushrooms.

Place the butter in a large saucepan and melt over
medium-low heat.  Peel and slice the garlic cloves, then add to the butter
and sauté for 2-3 minutes.

Add the mushrooms, turn the heat up to medium, and cover
with a lid.  The mushrooms will start to soften, and the moisture inside
the mushrooms will create its own juice.

Do not let the mushrooms dry out, so add a touch of vegetable stock if necessary.  After they have softened a little, add the sherry and herb de provence, and stir. Continue to sauté for another minute. 

Mix the milk and flour together in a small dish, then stir into the mushrooms.  I know milk might seem like an odd thing to add to mushrooms, but it smooths out the flavor of the garlic and sherry and adds a creaminess to the mushrooms. The mushrooms will thicken quickly, so watch them carefully, stirring every few seconds. Simmer for 1-2 minutes, then remove from the heat and serve immediately.