Scallop potatoes by slicing width-wise to create very thin circles. Thinly slice onion and separate into thin strips. Layer alternately: potatoes, onion, cheddar, dash of spices; repeat until casserole dish is 3/4 full. Top with cheddar. Pour milk into casserole until it's about 1/2 filled up the sides.
Bake at 350°F for about 1 1/2 hours until potatoes are tender (sometimes longer for thicker-cut potatoes). Test with fork, let sit for 10 minutes before serving.
Submitted by: Meghan Murphy