Preheat your oven to 375°F (190°C) and coat a 12-cup muffin pan with cooking spray.

Thinly slice the russet potatoes to about 1/16 inch thick using a mandoline or sharp knife.

In a large mixing bowl, melt the unsalted butter and combine it with olive oil, minced garlic, thyme, rosemary, sea salt, and black pepper.

Add the potato slices to the mixture and gently toss until every slice is thoroughly coated.

Layer the potato slices into the prepared muffin cups, overlapping them, and drizzle remaining mixture over the top.

Bake in the preheated oven for 45-50 minutes until golden brown and tender, rotating halfway through.

Let the galettes cool for about 5 minutes before removing them from the muffin pan.

Gently lift each galette out and transfer to a serving platter, garnishing with fresh herb sprigs if desired.