If the mushrooms aren't already split apart, separate them into individual "petals" (the fruiting body, including the cap and stipe). You can leave the small oyster mushrooms and cook them as is. If you're cooking King Oyster mushrooms, cut the caps off. Then slice the stipe into flat cylinders about 0.5 inch/1 cm thick (like what these egg tofu slices look like).
Heat the frying pan over medium heat. Add 4 tablespoons of butter. When the butter looks like it's half melted (meaning most of the butter is liquid but there is still some soft solid chunks), turn the heat down to low.
Add the chopped garlic into the butter. Stir to combine.
Add the chopped mushrooms to the garlic and butter.
Stir the mushrooms so they are coated in the garlic butter.
Leave the mushrooms to sauté in the garlic butter. The oyster mushrooms should begin to soften. If you're using pink oyster mushroms, they should begin turning gold. Keep the heat low such that you see the garlic and mushrooms sizzle around the edges but they are not turning brown quickly. If the garlic is turning brown within 2-3 minutes, turn the heat down to avoid burning the garlic.
Add the salt and pepper. Stir to combine. After adding the salt, the mushrooms should wilt further and release any liquid they may be holding.
The mushrooms should be cooked through by now. They are ready to serve. Optionally, you can caramelize them further if you're not in a hurry and want to add extra flavor.
If you want to caramelize the mushrooms, add the reamining 2 tablespoons of butter as the mushrooms have likely soaked up all the previously added fat.Spread the mushrooms into 1 layer with even spacing between them. Avoid stirring them too much as you want to give them adequate contact time with the hot pan to caramelize.
Allow the mushrooms to cook until they are browned on the edges. The butter should have also developed a golden brown color and a nutty aroma.
Flip the mushrooms once to caramelize both sides. Once the mushrooms are brown to your satisfaction, turn the heat off and allow the mushrooms to cook in the residual heat while you prepare to serve them.
Serve the sautéed oyster mushrooms as a side dish or a topping. Enjoy!