Preheat oven to 425° F.

Melt butter in a large ovenproof skillet over medium heat.

Add carrots and onion. Cook, stirring occasionally, for 4-5 minutes or until vegetables begin to soften.

Sprinkle flour over vegetables. Very slowly (starting with a tablespoon or two at a time) add milk and continuously whisk while adding milk until milk has been fully blended with flour and little to no lumps remain (should take the same amount of time as adding the milk, with maybe 30 seconds of whisking to fully workout the lumps). Continue to whisk and raise the heat to high to bring to a boil. Immediately reduce heat to a strong simmer (medium-low) and whisk every minute or two until milk mixture thickens (around 2-4 minutes).

Remove from heat and add thyme, peas, and turkey. Stir until combined.

Top with potato slices and bake for 20 minutes or until potatoes are soft and starting to brown.

Allow to sit for 5 minutes before serving.