Preheat oven to 400ºF. Heat a large sauté pan over medium-high heat; cook pancetta until crisp.
Drain excess grease and set aside.
Brush the insides of a muffin pan (8-12 portions) with 1 tbsp melted butter. Toss potato slices with remaining melted butter and season with salt, black pepper and thyme or oregano.
Place one potato slice in the bottom of each muffin cup; trim to fit if necessary. Top with a layer of onions, pancetta and gouda cheese. Place another potato on each stack pressing down and repeat with another layer of onions, pancetta, and gouda.
Top each stack with last slice of potato and remaining cheese. Bake for 25-30 minutes or until potatoes are tender and golden; remove from oven and serve hot.
Chef's Tip: Bacon can be used in place of pancetta if desired.