Mix the flour, salt, and sugar together in a large bowl. Add the butter. Using a pastry cutter, a food processor, or two forks, cut the butter into the mixture until you have pea-size crumbles with a few larger crumbs of fat. (I prefer a pastry cutter for control, ease, and so it’s not accidentally over-mixed.) Drizzle the cold water in, 1 Tablespoon (15ml) at a time, and stir after every Tablespoon added. Do not add any more water than you need to. Stop adding water when the dough begins to form large clumps. I always use about 3/4 cup (180ml) water. Transfer the pie dough to a floured work surface. Using floured hands, fold the dough into itself until the flour is fully incorporated into the butter pieces. The dough should come together easily and should not feel overly sticky. Form dough into a ball. Divide dough in half. Flatten each half into 1-inch thick discs using your hands. Wrap each tightly in plastic wrap. Refrigerate for at least 2 hours (and up to 5 days) or freeze for up to 3 months. Thaw overnight in the fridge before using.

Gently mix all of the filling ingredients together in a large bowl. Set aside.

Preheat oven to 375°F (190°C).

Remove 1 disc of pie dough from the refrigerator. Keep the other in the refrigerator as you work. I highly suggest rolling the dough out onto a piece of parchment paper or silicone baking mat fitted to your baking sheet. This way you can lift the entire piece of parchment/silicone baking mat off the counter (with the rolled out dough on top) and place on the baking sheet. Roll the dough out into a rectangle or oval shape. I find anywhere around a 10×16-inch size is great, though I’ve stretched it to a 13×18-inch size. Anywhere around this measurement will work. Dough should be about 1/8-inch thick. Make sure to turn the dough about a quarter turn after every few rolls. Carefully place the dough (with parchment/silicone baking mat) onto a large rimmed baking sheet.

Spoon filling evenly on top of crust, leaving any excess liquid in the bowl. Leave a bare 1-inch border around the edges.

Roll out the 2nd pie dough disc in the same-ish shape as the 1st. (If desired, you can cut into strips to weave a lattice on top.) Drape over filling, then use your hands to seal the top and bottom crusts together around the edges. Flute the edges or crimp with a fork. (See my how to crimp and flute pie crust tutorial if you need extra help with this step.) Cut slits into the top of the crust, then brush with a thin coating of egg wash. Sprinkle with coarse sugar, if desired.

Bake the slab pie for about 45-55 minutes until the crust is golden brown and you can see the filling bubbling. Remove from the oven and, if serving as handheld bars, allow to cool completely in the pan set on a wire rack. If serving on plates, allow to cool for at least 45 minutes in the pan set on a wire rack. This pie is fantastic served a little warm with vanilla ice cream or at room temperature (or as cold leftovers, yum!).

Cover leftovers tightly and store in the refrigerator for up to 3-4 days.