In a large mixing bowl, combine butter, flour, and sea salt. When the butter is evenly distributed, add in cold water and stir together. Roll the dough into a ball to wrap and refrigerate for 30 minutes.
Preheat oven to 375F. Prepare a standard sized muffin tin with oil spray or brush with oil.
In another large mixing bowl, mix together all the filling ingredients and leave to side.
Prepare a work surface with a sprinkle of flour and roll out dough on top. You may need more flour to prevent any sicking.
Use a round cookie cutter or an opened can (from your canned pumpkin puree) to cut out 10 round pieces of dough. Re-roll dough back into a ball and roll out again as needed until you maxed out the amount of circles you can cut out.
Fit a dough circle into each muffin tin, using your fingers to press down lightly. Fill each cup with pumpkin mixture until 2/3 full.
Bake for 18-20 minutes. The crust should turn a light golden brown and the filling will be slightly jiggly. Let mini pies cool in the pan before removing. Allow to cool in the fridge for 2-3 hours, and even overnight as they are best served cold! Top with whipped cream before serving!