Martha's Layered Crêpe Lasagna

I saw this recipe in the February issue of Martha Stewart Living and was inspired to try it. Gâteau de crêpes is like a savory crêpe lasagna with layers of crêpes and béchamel sauce with sautéed spinach and Gruyère cheese. I decided to make this dish for lunch this week, and although it is pretty involved and takes time to prepare and assemble, much of the steps can be done ahead of time and spaced out for convenience.

Source: Spinach-Gruyère Gâteau de Crêpes, Martha Stewart Living (February 2009)

Ingredients
½ medium onion, cut into ¼-inch dice
1 ounce (2 tablespoons) unsalted butter, plus more for sheet
2 tablespoons all-purpose flour
1 ½ cups whole milk
1 ¼ cups grated Gruyère cheese (4 ounces)
Pinch of freshly grated nutmeg
Coarse salt and freshly ground pepperFor the assembly:
2 tablespoons extra-virgin olive oil
3 garlic cloves, minced (1 tablespoon)
5 ounces baby spinach (about 6 cups)
Pinch of crushed red-pepper flakes
Coarse salt and freshly ground pepper
1 lemon, for squeezing
12 small Basic Crêpes

Directions
Make the béchamel: Place onion and butter in a medium saucepan over medium heat, and cook
until onion is translucent and softened, about 5 minutes. Add flour, and cook, stirring constantly, for 2 minutes. Whisk in milk in a slow, steady stream. Cook, stirring constantly, until mixture has thickened, about 5 minutes. Add 1 cup Gruyère, and stir until cheese melts. Remove from heat, add nutmeg, and season with salt and pepper.

To assemble: Heat oil in a large sauté pan over medium heat. Add garlic, and cook, stirring
occasionally, until softened, about 2 minutes. Add spinach, and cook, stirring occasionally, until wilted, about 2 minutes. Add red-pepper flakes, and season with salt, pepper, and a squeeze of lemon. Let cool slightly. Squeeze out any excess liquid, and coarsely chop.

Preheat oven to 450 degrees F. Reserve 2 tablespoons of béchamel. Mix remaining béchamel and spinach in a medium bowl. Butter a rimmed baking sheet. Place 1 crêpe on center of sheet, and top with 3 tablespoons spinach mixture, spreading evenly. Top with another crêpe, then 3 tablespoons spinach mixture. Repeat with remaining crêpes and spinach mixture, ending with a crêpe. Spread reserved béchamel on top, and sprinkle with remaining ¼ cup cheese. Bake until cheese melts and turns golden brown, 10 to 12 minutes. Let cool slightly, then transfer gâteau de crêpes to a platter. Cut into wedges, and serve warm.