Spray a standard-size pie pan with non-stick cooking spray and rub with a paper towel to coat. Add 1 teaspoon of soft butter and rub again with the paper towel to evenly coat.

Unroll the refrigerated pie crust and pat it with your hands into a flat circle. Pick up the crust and center it in the prepared pan. Press the dough into the pan and up over the edges. It will extend about a half inch over the top edges of the pan.

Turn the excess dough under to form a lip that extends about a half inch above the upper edge of the pan. Crimp the edges of the dough to form a scalloped ridge around the top of the pan.

Whisk the egg vigorously in a small bowl or cup. Brush the interior of the crust with the egg. Place the crust in the refrigerator for at least an hour (or up to 24 hours to chill).

Preheat the oven to 425 degrees F (220˚C) with one of the shelves on the lowest rack and one in the center. Place a sheet pan on the lowest rack while the oven preheats.

Combine the sugar and flour in a large bowl. Stir to combine.

Add the blackberries and stir to coat. Keep stirring until the berries are well coated. There will be a little extra flour/sugar at the bottom of the bowl. Sprinkle the berries with the lemon juice then gently stir again until there is no more dry flour.

Spoon the mixture into the prepared pie shell. The berries should form an even layer about a half inch below the ridge of the crimped crust. If there are any empty spaces, tuck in a few more berries.

Place the pie tin on top of the preheated sheet pan on the lower oven rack. Bake for 15 minutes then remove from the oven to add the crumble.

While the pie is starting to bake, make the crumble: Place the butter in a medium-large microwave-safe bowl. Cover the bowl with a damp paper towel. Cook on high power for 1-2 minutes, until the butter is melted.

Remove the paper towel and add the remaining crumble ingredients to the melted butter. Stir the mixture with a fork until large crumbs form. Set aside.

After the pie has baked on the lower shelf for 15 minutes, remove the sheet pan (with the pie on top of it) and reduce the oven temperature to 375.

Using your hand, grab a handful of the crumble mixture and give it a squeeze to break it up into large crumbs as you sprinkle it over the top. Continue with the remaining crumble, covering the top of the pie.

Return the pie to the oven, on the center rack this time, and bake for another 20-30 minutes until the filling is bubbling and the crust is golden brown.

Cool on a cooling rack for at least an hour before serving. Serve and enjoy with a scoop of vanilla ice cream.