Place onion, chicken, butter, garlic, carrots, potatoes, and cauliflower in a slow cooker in that order. Sprinkle curry powder, turmeric, chile flakes, ginger, salt, and pepper on top. Add enough chicken stock to mostly cover the contents of the slow cooker.

Cook on Low, stirring periodically if you are home, about 8 hours.

Stir flour into the slow cooker and let simmer until the sauce thickens a bit, 10 to 15 minutes.