Preheat oven to 375 degrees F (190 degrees C). Grease a 2-quart casserole with butter.
Heat canola oil in a skillet over medium heat; cook and stir onion until translucent, about 5 minutes. Stir ground beef into onion, season with salt and black pepper, and cook ground beef mixture until browned and crumbly, about 10 more minutes. Drain excess grease.
Spread cooked ground beef mixture into bottom of the prepared casserole dish; pour cream-style corn over the ground beef in a layer; top with layer of mashed potatoes.
Bake in the preheated oven until potatoes are browned and casserole is bubbling, about 30 minutes.
