As an exception to most baking, make sure to use ingredients as cold as possible when making pastry: so cubed butter straight from the fridge and ice cold water. Keeping pastry cold helps avoid overworking the gluten and keep it relaxed to avoid shrinkage during baking.
Handle the pastry dough as little as possible throughout making. This is especially important when bringing it together, as overworking the gluten will lead to tough pastry.
When placing the pastry circles into the tin, try not to stretch the dough to make it fit. Stretching the dough may look fine one in the tin, but it will shrink back to its pre-stretched state, resulting in uneven cases for the mini pies.
Chill the pastry shells again once rolled and shaped into the tin. Chilling the pastry a second time will allow the gluten to relax again, helping it hold its shape better and not be tough once baked.
Fill the pastry shells to near the top with pumpkin pie filling. Once filled, give the tin a gentle jiggle or tap to level the tops and release any air bubbles trapped before baking.
The pumpkin pie is baked when the edges of the pastry are golden and the middle of the filling still has a slight wobble. Remove from the oven but leave the pies in the tin to cool completely and firm up.
Once cool, store these mini pumpkin pies in the fridge undecorated. Top with whipped cream and a dusting of pumpkin spice just before serving.