How to Make It
In a saucepan over a medium heat, cook blackberries, 1 ¼ cup water, cornstarch and sugar until thick, stirring occasionally. Add lemon juice, butter, salt and nutmeg and stir until butter is melted and incorporated. Remove from heat and let cool to room temperature.
Preheat oven to 400°F.
To prepare crust, divide chilled pie dough in half (one for the bottom crust, one for the top crust). Return unused half to the refrigerator. Roll out the dough on a lightly floured surface to ¼ inch thickness and 12-inch diameter if you are using a 9-inch pie pan. Line the bottom of your pie pan with the dough leaving any over-hanging dough. Chill in refrigerator while you roll out the top crust.
For the top crust, roll out the remaining chilled dough on a lightly floured surface to ¼ inch thickness. Using a 1/2-inch star cookie cutter, cut 15 to 20 stars out of the dough and place them on a parchment-lined cookie sheet. Bake until just golden brown, 7 to 10 minutes. Remove from oven and allow to cool completely.
Pour cooled blackberry pie filling into bottom crust that has been in the refrigerator.
Place the pie on a baking sheet (to catch any spillage during baking) and bake at 400 degrees for 10 minutes. Reduce heat to 350 and bake for 30 minutes. If needed, place a sheet of aluminum foil over the pie (or use a pie protector) to protect the edges and tops from getting too burnt.
Remove pie from oven and place cooled star cut-outs in desired design on top of blackberry filling. Allow to cool to room temperature before serving.