Preheat your oven to 375°F (190°C). Grease a 12-cup muffin pan generously with cooking spray to prevent sticking.

Thinly slice your russet potatoes to approximately 1/16 inch using a mandoline or a chef's knife.

In a large mixing bowl, combine melted unsalted butter, olive oil, minced garlic, chopped fresh thyme, chopped fresh rosemary, fine sea salt, and freshly ground black pepper. Stir well until all ingredients are blended.

Toss the sliced potatoes in the herb mixture until each slice is evenly coated.

Layer the coated potato slices in each muffin cup, filling them generously. Drizzle any remaining herb mixture on top.

Bake in your preheated oven for 45-50 minutes, until golden brown and tender. Rotate the muffin pan halfway through.

Let stand for about 5 minutes after removing from the oven. Carefully transfer the galettes onto a serving platter, garnishing with fresh herb sprigs.