Preheat the oven to 425 degrees.
Squeeze as much water out of the thawed spinach as possible.
Finely chop up the spinach.
Heat the olive oil in a large saucepan over medium heat.
Add the shallot, garlic, and serrano (if using), stirring occasionally until softened, approximately 5 minutes.
Add the milk and cream cheese, whisking to melt and incorporate evenly.
Once fully melted, reduce the heat to low and whisk in the monterey jack cheese.
Once the monterey jack cheese is fully incorporated, stir in the spinach and corn.
Season to taste with salt and pepper.
Transfer the dip to an ovenproof serving dish and sprinkle with the remaining ¼ cup monterey jack cheese.
Bake for 10 minutes, and then broil for an additional 1-2 minutes for a golden, bubbly crust.
Serve immediately with pita or tortilla chips.
