Preheat oven to 350°F (175°C). Melt butter in a skillet over medium heat, add squash, onion, salt, and pepper, and cook for 10 minutes until tender. Drain excess liquid.

In a large bowl, combine sour cream, cheddar, garlic, and a pinch more salt and pepper. Fold in the squash mixture.

Spread filling in a greased 8x8-inch baking dish. Crush Ritz crackers and toss with melted butter, then sprinkle evenly over the top.

Bake for 25 to 30 minutes until bubbling and golden. Broil briefly if needed for extra browning.

Let rest 5 minutes, then scoop and serve warm.