In a large mixing bowl, you will need to whisk together the flour and salt. Thereafter, add the cubed butter and use a pastry cutter or your fingers to cut the butter into the flour mixture until it resembles coarse crumbs.
In a small bowl, whisk together the egg yolk and ice water, then pour this mixture into the flour mixture and stir until the dough comes together in a ball.
Turn the dough out onto a floured surface and knead it for a minute or two until it becomes smooth. You will then need to form the dough into a disc and wrap it in plastic wrap. Chill it in the refrigerator for at least 30 minutes.
Preheat your oven to 375°F (190°C) and grease a 24-cup mini muffin tin with cooking spray.
Roll out the chilled dough on a floured surface until it is about 1/8 inch thick. Thereafter, use a round cookie cutter or a glass to cut out circles of dough that will fit into the muffin tin cups. Press the dough circles into the muffin cups and use a fork to prick the bottoms a few times.
Bake the pastry shells for 10-12 minutes or until they are lightly golden brown. Remove them from the oven and set them aside to cool while you prepare the filling.
In a large mixing bowl, whisk together the eggs, heavy cream, and milk until they are well combined. Then you will need to add the grated cheese, diced ham or bacon, diced bell pepper, and diced onion to the bowl and stir to combine. Season the mixture with salt and pepper to taste.
Pour the filling mixture into the cooled pastry shells, filling them about 3/4 of the way full. Bake the quiches for 15-20 minutes or until they are puffed up and golden brown.
Remove the quiches from the oven and let them cool in the muffin tin for a few minutes. Use a butter knife or small spatula to gently loosen the quiches from the muffin cups and transfer them to a wire rack to cool completely.
Serve the mini quiches warm or at room temperature, garnished with fresh herbs if desired.