Make the cowboy butter: In a mixing bowl combine softened butter, Dijon, lemon juice, garlic, parsley, chives, thyme, paprika, cayenne, and red pepper flakes. Mix until smooth and well combined; taste and season lightly with salt and pepper.

Prep mushrooms: Wipe mushrooms clean with a damp towel or soft brush and pat very dry. Halve or quarter larger pieces so sizes are similar.

Heat a large skillet over medium-high. Add the olive oil (if using) and 1 to 2 tablespoons of the cowboy butter; allow it to melt and foam.

Sauté in batches: Add about half the mushrooms in a single layer. Let them cook undisturbed for 2–3 minutes to brown, then toss. Cook 8–10 minutes total, adding a spoon of cowboy butter as needed, until golden and tender. Transfer to a bowl and repeat with remaining mushrooms.

Glaze and finish: Return all mushrooms to the skillet with another spoonful of cowboy butter. Toss until glossy. Season to taste with salt and black pepper and add a final squeeze of lemon.

Serve warm as a side or topping. Garnish with extra herbs and Parmesan if desired.