Set a baking dish filled with 1 inch of water on the bottom oven rack. The water creates a gentle steamy environment that helps the egg bites bake up soft instead of drying out.

Heat the oven to 300 °F, then coat a mini muffin pan well with oil or line it with silicone liners. The pan should be fully prepped before the egg mixture goes in, since baked eggs stick fast once they set.

Scatter the chopped spinach, crumbled bacon, and shredded cheddar evenly into the muffin cups. Putting the fillings in first helps distribute them cleanly so each bite gets a little of everything.

Whisk the eggs, heavy cream, sea salt, and black pepper together in a large bowl until just combined. The mixture should look smooth and unified, not frothy or full of bubbles.

Pour the egg mixture into the prepared mini muffin pan, dividing it evenly among the cups. If you tap the pan gently on the counter, any larger trapped air bubbles will rise and the tops will bake more evenly.

Bake the pan on the middle rack for 20 min, until the centers are just set. The tops should look slightly domed and feel springy, with no wet shine in the middle.