To make the crust: Combine the flour and 1/8 teaspoon salt into a bowl and cut into the butter with a pastry blender or fork until the mixture resembles crumbs. Stir in 2 to 3 tablespoons ice water, 1 tablespoon at a time, until the flour is just moistened. Gather the dough into a ball and wrap in plastic and refrigerate for at least 15 minutes or overnight.
Preheat the oven to 375 degrees. Roll out the dough on a lightly floured surface into a 9-inch rectangular, square or round pan. Crimp or flute the edges.
To make the chard: Film a deep sauté pan with the oil and set over medium-low heat. Add the chard stems, onions and garlic and cook until soft, about 5 minutes. Add the chard leaves, red pepper flakes, and salt and pepper to taste. Cover and continue cooking, stirring occasionally, until the leaves are very tender, about 8 to 10 minutes. Remove the lid and adjust the seasonings.
Place the chard into the prepared pie. Dot with tablespoons of the cheese, and bake until the crust is golden and the cheese is bubbly and nicely browned, about 25 to 30 minutes. Serve warm or at room temperature.
Nutrition information per serving: