Sturdy escarole can stand up to casserole treatment. Prepare to battle it out for the addictive breadcrumb topping.
Preheat oven to 400 degrees. Place a colander in a large bowl. Bring a large pot of salted water to a boil. In 2 batches, cook escarole until tender, 7 minutes, then drain in a colander, pressing with a spatula to squeeze out as much liquid as possible.
In a small saucepan, melt 1 tablespoon butter over medium. Cook shallot and garlic until tender, 4 minutes. Add flour and cook, stirring, 1 minute. Whisking constantly, add milk and cook, whisking, until mixture comes to a boil and thickens, 2 minutes. Remove from heat, season with salt and pepper, and stir in escarole. Pour mixture into a 1-quart baking dish.
In a food processor, pulse bread until coarse crumbs form; transfer to a small bowl. Melt 1 tablespoon butter and pour over breadcrumbs, stirring to combine. Season with salt and pepper. Top escarole with breadcrumbs and bake until golden brown and bubbling, 15 to 20 minutes.
Green Mix You can use kale, chard, or spinach in place of some or all of the escarole in this dish.