Preparation Method
- Make the crust and blind bake: Follow the instructions for rolling, chilling, and blind baking the piecrust. Set aside.
- Make the topping: In the mixing bowl of the stand mixer fitted with the flat beater attachment, beat butter and sugars on medium-low (3–4) speed until well blended, about 2 minutes. Scrape down the bowl. Add flour and beat on low (1–2) speed until coarse crumbs start to form. Add oats and pulse until blended. Set aside.
- Make the filling: In a large bowl, stir together strawberries, blackberries, blueberries, raspberries, sugars, lemon juice, and lemon zest. Add flour and toss until the berries are coated.
- Preheat the oven to 375°F (190°C) with a rack set in the middle position.
- To assemble, pour the berry mixture into the prepared piecrust and cover with the crumb topping. Place a pie guard over the edge of the crust. Bake until the pie filling is bubbling in several spots at the edge of the crust, 55–60 minutes. Let cool on a wire rack for 1 hour or until ready to serve.
Pro Tip
Use cold butter in the crumb topping so the flour and oats adhere to the butter and remain atop of the pie while baking to create the quintessential crumb layer. If the butter is too soft, the topping will sink into your pie.
