Rub olive oil on all sides of the slow cooker. You may also use an oil spray. Distribute the potatoes, onions, jalapeno, and salsa inside the slow cooker.: The warm metal will smell faintly fruity as the olive oil heats, creating a subtle toasty note and preventing sticking. I like to use just enough to coat the interior so the casserole pulls away easily when served. If you skip this, the edges can adhere and tear when you try to lift portions out, so don't skip the oil step. Watch for pooled oil at the bottom, which signals too much added fat.
In a separate bowl, lightly whisk the eggs. Add the mozzarella, salt, and pepper. Pour this mixture into the slow cooker, being sure to cover the potatoes.: As you layer the thinly sliced potatoes , diced onion , and diced jalapeño , you'll notice the fresh vegetal scent building, with the onion sweetness softening as it nestles between slices. Even distribution ensures each serving has a balanced bite. A common error is piling a single ingredient in one spot, which leads to uneven cooking; spread items out evenly for consistent tenderness.
Set the slow cooker on low for 4 hours, or until potatoes are tender and the eggs set.: Whisking the eggs until the whites and yolks are just combined creates a silky custard. The mixture should look homogenous, with small streaks of air that translate to a tender set. Overwhisking introduces too much air and can make the finished texture spongy instead of creamy, so stop once blended.
Add the mozzarella, salt, and pepper: Folding in the grated mozzarella , measured salt , and black pepper distributes flavor pockets that melt as the dish cooks. The cheese will later form melty ribbons, while the salt seasons the whole custard. Be careful not to over-salt at this stage, because cheeses can concentrate flavors as they reduce.
Pour this mixture into the slow cooker, being sure to cover the potatoes: When you pour, watch as the egg mixture sinks into the layers, surrounding the potatoes and filling voids. You should hear a quiet settling sound and see the surface even out. Ensuring coverage helps the potatoes cook evenly and prevents dry edges. If the top remains dry in spots, gently nudge the filling with a spatula so the custard settles into those areas.
Set the slow cooker on low for 4 hours, or until potatoes are tender and the eggs set: Over the long, steady cook, the kitchen fills with baked egg and warm starch aromas, and you may notice gentle bubbling at the edges as the casserole finishes. The eggs should be set but still slightly tender in the center when you test with a knife, which should come out mostly clean. A common mistake is opening the lid too often, which releases heat and extends cooking time; resist peeking for best results.
