Prepare my butter pie crust recipe through step 5.

Whisk the brown sugar, flour, cinnamon, and salt together in a medium bowl. Cut in the butter using a pastry cutter or forks until the mixture is crumbly. Stir in the oats. Refrigerate until ready to use.

After the pie dough chills, preheat the oven to 400°F (204°C).

Roll out the chilled pie dough onto a lightly floured surface. Remember, when rolling out the pie dough, always use gentle force with your rolling pin. Start from the center and work your way out in all directions, rotating the dough with your hands as you go. Roll it out into a circle 12 inches in diameter. Carefully place the dough in a 9-inch pie dish. Tuck it in with your fingers, making sure it’s smooth. For a beautiful edge, fold the overhanging dough back over the edge and use your hands to mold the edge into a nice thick rim around the pie. Crimp the edges with a fork or use your fingers to flute the edges. For visuals and a video of this, see how to crimp and flute pie crust. Brush the edges with egg wash. Refrigerate for at least 10 minutes as you prepare the pie filling. This helps keep the crust cold and prevents shrinking.

In a large bowl, combine the blueberries, sugar, flour, cornstarch, lemon juice, and lemon zest. Mix together until it’s no longer dry and powdery; burst a few blueberries if necessary to moisten. See photo above for a visual, if needed.

Spoon the filling into the crust. Top evenly with the cold crumble topping.

Place the pie on the center oven rack. Place a baking sheet on a rack below it, to catch any juices that may bubble over. Bake the pie for 25 minutes. Then, keeping the pie in the oven, reduce the oven temperature to 375°F (190°C). Place a pie crust shield (see Notes for homemade shield) on the edges to prevent them from over-browning. Continue baking the pie until the filling is bubbling around the edges, 35–40 more minutes. If you want to be precise, the internal temperature of the filling taken with an instant-read thermometer should be around 200°F (93°C) when done. Tip: If needed towards the end of bake time, remove the pie crust shield and tent an entire piece of foil on top of the pie if the top looks like it’s getting too brown.

Remove pie from the oven, place on a cooling rack, and cool for at least 4–5 hours before slicing and serving. Filling will be too juicy if the pie is warm when you slice it. Slice and serve with vanilla ice cream, if desired.

​​Cover and store leftover pie at room temperature for up to 1 day or in the refrigerator for up to 5 days.