Preheat your oven to 350°F (175°C).
In a mixing bowl, combine the flour, softened butter, sugar, and salt. Use a pastry cutter or your fingers to mix until the mixture becomes crumbly.
Gradually add cold water, one tablespoon at a time, until the dough comes together. Be careful not to overwork it.
Roll out the dough on a floured surface to about ⅛ inch thick. Use a cookie cutter or glass to cut out circles of dough that will fit into the muffin tin cups.
Gently press the dough circles into the muffin tin, making sure to cover the bottom and sides.
In another mixing bowl, whisk together the pumpkin puree, sweetened condensed milk, egg, cinnamon, nutmeg, ginger, and salt until smooth and well combined.
Fill each mini crust with the pumpkin filling, being careful not to overfill.
Bake in the preheated oven for about 30 minutes, or until the filling is set and the crust is lightly golden.
Remove from the oven and allow to cool slightly before carefully removing the mini pies from the muffin tin.
Serve warm or at room temperature, and enjoy!