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 into a flat circle. Center it in the prepared pan and press it into the pan and up over the edges.

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 to form a scalloped ridge around the top of the pan.

Whisk the egg and brush the interior of the crust with it. Place in the refrigerator to chill for at least an hour.

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

Combine the sugar and flour in a large bowl, then add blackberries and stir to coat.

Sprinkle the berries with lemon juice and stir again until there is no more dry flour.

Spoon the mixture into the prepared pie shell, creating an even layer about a half inch below the ridge.

Place the pie tin on the preheated sheet pan and bake for 15 minutes.

Melt butter in a microwave-safe bowl covered with a damp paper towel for 1-2 minutes.

Add the remaining crumble ingredients to the melted butter and stir with a fork until large crumbs form.

After the pie has baked for 15 minutes, reduce the oven temperature to 375 degrees F (190˚C) and sprinkle the crumble over the pie.

Return the pie to the center rack 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.