01 - Generously grease the interior of the crockpot insert with butter to prevent sticking and ensure easy serving.
02 - Melt 2 tbsp butter in a small saucepan over medium heat. Add minced garlic and sauté until fragrant, approximately 1 minute. Sprinkle in flour and cook constantly stirring for another minute to form a roux. Gradually whisk in cream and milk until fully incorporated and smooth. Bring the mixture to a gentle simmer, then remove from heat. Stir in salt, pepper, and half the cheddar cheese until completely melted and smooth. Set aside.
03 - Arrange half the sliced potatoes in an even layer at the bottom of the prepared crockpot, overlapping slices slightly as needed. Distribute half the chopped onion evenly over the potatoes, followed by half of the remaining cheese. Pour half the cheese sauce over this layer, ensuring even coverage.
04 - Repeat the layering process with remaining potatoes, onion, cheese, and sauce. Sprinkle paprika over the top layer for added color and flavor if desired.
05 - Cover the crockpot and cook on high setting for 4 hours or low setting for 7 hours. The dish is complete when potatoes are fork-tender and the top is golden and bubbly.
06 - Remove the lid and allow the scalloped potatoes to rest for 10 minutes before serving. This resting period helps the sauce thicken slightly and makes serving easier. Garnish with freshly chopped parsley just before serving.