Spread the cooked, crumbled sausage evenly over the bottom of the prepared baking dish, making sure it’s in a single layer so every bite gets some sausage.
In a medium mixing bowl, whisk together the eggs and heavy whipping cream until the mixture is smooth, well combined, and slightly frothy. Season lightly with salt and pepper only if your sausage is not very salty; many breakfast sausages are already highly seasoned.
Stir 1 1/2 cups of the shredded cheddar cheese into the egg and cream mixture, reserving the remaining 1/2 cup for the top.
Pour the egg, cream, and cheese mixture evenly over the sausage layer in the baking dish, gently shaking the dish if needed to help the liquid settle around the sausage.
Sprinkle the remaining 1/2 cup shredded cheddar cheese evenly over the top. This will help create that golden, bubbly, slightly crispy top with browned edges and a soft, tender center.
Bake in the preheated oven for 30–40 minutes, or until the quiche is puffed, the edges are nicely browned, the center is set, and a knife inserted near the center comes out mostly clean with no runny egg. The top should look golden with little brown spots from the cheese and sausage.
Remove the quiche from the oven and let it rest for 5–10 minutes before slicing. This helps it firm up slightly so you get clean squares while keeping the interior fluffy and moist. Slice into 6 pieces and serve warm.
