Cook the pork breakfast sausage pieces in a skillet at medium-high heat until the pan reaches about 400°F equivalent and brown the meat for 8 to 10 minutes. Break it apart with a wooden spoon in short presses, then fold in the diced yellow onion for the final 3 minutes. (I tried adding raw sausage once. The casserole released too much grease, so browning first fixed the texture.) You'll see deep golden sausage bits and soft onion pieces with a savory smell. Don't rush it. Miss this window and excess fat can make the eggs watery. Browning first builds flavor while removing extra moisture.

Spread shredded russet hashbrowns in a slow cooker in loose layers, then add browned pork breakfast sausage, diced yellow onion and shredded sharp cheddar. Whisk the eggs and whole milk for 2 to 3 minutes with a fork until blended, then pour the mixture evenly over the layers. The temperature stays at room level during assembly and the layering takes about 10 minutes. The hashbrowns shift into soft overlapping layers while the egg mixture settles between the pieces. You'll notice a creamy yellow mixture around the edges. Skip the even pour and some sections may stay dry.

Cook the layered casserole on low heat, about 200°F inside the slow cooker, for 6 to 7 hours until the eggs set. Keep the lid closed and avoid stirring because the layers need time to firm. Check near hour 6 by gently pressing the center with a spoon to test the structure. The top turns lightly golden and the edges become firmer while the middle stays tender. You'll smell the melted cheddar and sausage blend together. Open the lid too often and the heat drops, which delays setting. Slow heat lets the egg proteins set evenly without drying the edges.

Rest the casserole for 15 minutes after cooking at about 200°F slow cooker heat, then cut a portion with a sharp knife. Lift one serving carefully and place it on a plate while keeping the layers together. (My first batch was served immediately and the center slid apart. The short rest made the slices hold.) The slice shows melted cheese pockets, tender eggs and golden hashbrown edges. The smell stays rich and savory. Skip the rest and the filling may separate. Resting gives the proteins time to hold the layers.