Make the crust: In a large bowl, combine the flour and salt. Use a pastry blender to cut in the butter until the mixture becomes crumbly. Add water 1 Tbsp at a time, toss with a fork until mixture becomes moistened. Shape the mixture into a ball, cover, and chill for 1 hour.

Preheat the oven to 400 degrees Fahrenheit. Roll the crust out into a 10 inch circle. Use a 3 inch cookie/biscuit cutter to cut out 8 to 9 circles. Roll each circle out large enough to fit inside the cup of a large 6-cup muffin pan. Gently press dough circles into the cups of the muffin pan. Cover with plastic wrap and refrigerate until ready to use.

Melt the butter in a skillet over medium heat. Add the squash, leek, and salt. Cook until the leeks are soft and transparent, about 8 minutes.

Whisk together the eggs, cream, salt, white pepper, and Dijon mustard. Stir in the cheese. Pour ⅓ cup of the mixture over each crust. Divide squash mixture evenly over the filled crusts.

Bake for 40 to 45 minutes, until cheese is golden brown. Allow to cool for 10 minutes before serving.