When I originally developed this mixed berry slab pie recipe, we were in prime rhubarb season, and, alas, now that I am finally posting it, we are most decidedly not. However, one can easily substitute mixed berries for the rhubarb, and no one will be any the wiser.
This berry slab pie, despite what you might be thinking about the inclusion of rhubarb, is all that and then some. The crust is more tart or cookie-like, than pie like – and by that I mean you press it into your pan, reserving some of the mixture with which to make a crumb topping . . . Which means the whole darn thing can be assembled awfully quickly.
And can be eaten out of hand once baked, if that’s your thing . . . But I do love it with a dribble of cold heavy cream, so I tend to eat mine off of a plate . . . 
This mixed berry slab pie recipe was first published in Main Street Magazine.
Easy-Peasy Mixed Berry Slab Pie
Ingredients
For the crust:
- 2 2/3 cups all-purpose flour
- 1/2 cup granulated sugar
- 3/4 tsp table salt
- 3/4 cup unsalted butter cold and cubed
- 1 yolk
- 1 tsp pure vanilla extract
- 1/4 cup cold water
For the crumb topping:
- 1 cup all-purpose flour
- 1/2 cup granulated sugar
- 1/2 tsp table salt
- 1/2 tsp baking powder
- 1/2 cup unsalted butter cold and cubed
For the filling:
- 5 cups rhubarb sliced, fresh or frozen
- 5 cups mixed berries fresh or frozen
- 3/4 cup corn starch
- 1 3/4 cups granulated sugar
- 1/4 tsp table salt
- Confectioners’ sugar for dusting
Instructions
To make the crust:
- Preheat the oven to 400-degrees.
- Grease a 13x9x2-inch pan with cooking spray or softened butter. Line with parchment and grease again. Set aside.
- Combine the flour, the granulated sugar, and salt in the bowl of a food processer fitted with the metal blade and pulse to combine.
- Add the cubed butter to the bowl, and pulse until coarse crumbs form. Add the egg yolk, vanilla, and water and process until the dough begins to come together asa cohesive mass.
- Transfer the dough to the prepared pan and evenly press it into the bottom and two-thirds of the way up the sides of the pan. It may seem like there is not enough dough, but there is.
- Place in the freezer wrapped in plastic wrap while you assemble the filling and crumble, or for up to three days.
To make the crumb topping:
- In the same bowl of the food processor (no need to clean it), add theflour, granulated sugar, salt and baking powder, and pulse to combine.
- Add the cubed butter to the bowl, and process until a cohesive mass forms. Transfer to a bowl, cover with plastic wrap, and place in the refrigerator until ready to use.
To make the filling:
- Combine the rhubarb, mixed berries, corn starch, granulated sugar, and salt in a large bowl and mix together.
- To assemble the pie, place the filling in the crust and top with the crumble. Bake for 60 to 80 minutes, less time if you are using fresh rhubarb and berries, rotating the pan after 30 minutes, and tenting the top with aluminum foil. At 60 minutes, remove the foil and if the center is not yet bubbling and the crumb is not yet brown, continue baking the pie.
- The pie is ready when the filling is visibly bubbling in the center, looks set, and the crumble is nicely browned. Let cool to room temperature before dusting with confectioners’ sugar and serving (with vanilla ice cream, of course).