This tart, which comes from baker Nick Malgieri, uses a salty, smoky ham known as speck, a traditional ingredient in this tart; bacon is a good substitute.
For the Crust
- 1 1⁄2 cups flour
- 1⁄2 tsp. baking powder
- 1⁄4 tsp. kosher salt
- 8 tbsp. unsalted butter, chilled and cubed
For the Filling
- 3 oz. speck or bacon, finely chopped
- 3 tbsp. unsalted butter
- 1 1⁄2 lb. white onions (about 3), finely chopped
- Kosher salt to taste
- 1⁄2 cup milk
- 1⁄2 cup heavy cream
- 3 eggs
- 3 oz. grated Gruyère or Swiss cheese
- Freshly ground black pepper and freshly grated nutmeg
Make the crust: Pulse flour, baking powder, and salt in a food processor to combine. Add butter and pulse until pea-size pieces form. Add 1⁄4 cup ice-cold water; pulse briefly. Transfer dough to a floured work surface; form into a disk. Wrap in plastic wrap; chill for 1 hour.
Heat oven to 425°. Transfer dough to a floured work surface. Roll dough into a 13" circle; transfer to an 11" fluted tart pan with a removable bottom, pressing into bottom and sides. Trim excess dough; chill for 30 minutes. Prick bottom of dough with a fork; cover bottom with a sheet of parchment paper; fill with dried beans. Bake until crust is set, about 20 minutes. Remove paper and beans; bake until crust is light brown, about 15 minutes. Let cool.
Meanwhile, make filling: Cook bacon in a 4-qt. saucepan over medium heat until crisp, 7–8 minutes. Using a slotted spoon, transfer bacon to a plate. Discard bacon fat; add butter. Add onions and season with salt; reduce heat to low, cover, and cook, stirring occasionally, until soft, about 10 minutes. Uncover; cook until lightly browned, 10 minutes. Let cool.
Whisk milk, cream, and eggs in a bowl; add reserved bacon and onions along with cheese. Season with salt, pepper, and nutmeg. Pour filling into tart; place on a baking sheet. Place tart in oven and reduce heat to 400°. Bake until filling is golden brown and set, 45–50 minutes. Transfer tart to a wire rack to let cool completely before slicing and serving.