• Preheat the oven to 375ºF. Spray a 9x13-inch casserole dish with nonstick cooking spray. Set aside.
• Use a mandoline* to slice each potato into 1/8-inch thick rounds. We used size 2.0 on our mandoline. Set sliced potatoes aside.

Make the Cheese Sauce

• Heat 1 tablespoon of olive oil in a medium saucepan over medium/high heat. When the olive oil is fragrant, add the onion and 1/4 teaspoon salt to the saucepan and sauté for 3 minutes. Add the garlic and sauté for another 2-3 minutes or until the onion begins to brown.
• Mix in the last 3 tablespoons of olive oil to the pan and let it heat for 30 seconds.
• Add the flour to the saucepan and whisk the oil, onion, garlic, and flour together until it turns into a paste.
• While whisking, slowly pour the milk into the saucepan. Continue to whisk the milk over medium heat until the milk begins to thicken.
• Remove the saucepan from the heat and sprinkle the cheddar cheese into the saucepan. Whisk until the cheese melts.
• Add the vegetable broth, garlic powder, and Greek Yogurt to the saucepan and whisk until combined.

Assemble the Scalloped Potatoes

• Spread 1/2 cup of the cheese sauce into the bottom of the prepared casserole dish.
• Use the sliced potatoes to create 3 rows of tightly packed potatoes on top of the cheese sauce in the dish.
  
• Carefully pour the cheese sauce on top of the potatoes, working the cheese sauce in between each potato round. You can use a knife or fork for this, but it's important to get the cheese in between each potato slice and on top. This is a tedious step but the effort is well worth it!
  
• Cover the baking dish with foil and bake for 30 minutes.
• Remove from the oven, scrape down the sides of the dish, and bake (covered) for an additional 15 minutes.
• Remove the baking dish from the oven and sprinkle the parmesan cheese on top of the potatoes.
• Turn the heat to 450ºF and place the casserole dish, uncovered, back in the oven for 5 minutes or until the parmesan cheese starts to brown.
• Garnish with fresh thyme and let potatoes rest for at least 5 minutes before serving to allow the sauce to thicken.