Heat large deep nonstick skillet over medium-high heat.
Working in batches (about 10 cups at a time), sauté fresh spinach in dry skillet until bright green and wilted, about 2 minutes per batch.
Transfer spinach to strainer.
Squeeze spinach dry; roll in kitchen towel to remove excess water.
Melt butter with oil in heavy large skillet over medium heat.
Add leeks, shallot, and garlic; cook until soft, about 5 minutes.
Remove from heat.
Whisk cream and eggs in large bowl to blend.
Whisk in all cheeses, salt, and pepper.
Stir in spinach, leek mixture, and 2/3 of roasted red peppers (reserve 1/3 of peppers for topping).
(Can be prepared 1 day ahead. Cover and refrigerate.) Preheat oven to 350.
Generously butter 13x9x2-inch baking dish.
Transfer spinach mixture to prepared dish.
ake gratin until knife inserted into center comes out clean, about 50 minutes.
Arrange remaining red pepper strips decoratively atop gratin and serve.
This is soooooo not your typical creamed spinach.