Heat butter in a large skillet over medium-high heat until it begins to foam and sizzle. Add mushrooms then stir to coat. Saute until the mushrooms release their liquid then add garlic and continue to saute until the liquid has evaporated and the mushrooms are golden brown, 10-12 minutes. Stir occasionally and monitor temperature to ensure mushrooms are lightly sizzling and garlic doesn't burn.
Drizzle on desired amount of tamari — start with 1 teaspoons — then stir to combine. Taste then add salt if necessary, and then serve.
Notes
I added chopped fresh parsley for a little color which is completely optional.