In a large bowl, mix flour and salt together. Using a pastry cutter or fork, work the butter into the flour mixture until it resembles coarse crumbs. Add ice water, 1 Tbsp at a time, until the dough just comes together (around 5 Tbsp). Form the dough into a ball, wrap in plastic, and chill for at least 30 minutes.

Preheat the oven to 425°F. In a large bowl, combine strawberries, rhubarb, granulated sugar, brown sugar, salt, and cinnamon. Then, add cornstarch, flour, orange zest, orange juice, and vanilla extract. Mix well and set aside.

In another bowl, mix flour and brown sugar together. Using a fork or pastry cutter, work the butter into the mixture until it forms coarse crumbs.

On a floured surface, roll out the dough into a large rectangle, slightly larger than your sheet pan. Transfer the dough to the sheet pan by loosely wrapping it around your rolling pin and then unrolling it over the pan. Gently press the dough down into the baking sheet, leaving about 1/2” of overhang. Tuck the extra dough underneath to create a thick crust edge, and then crimp the edges.

Pour the filling into the crust, spreading it evenly. Top with the brown sugar crumb mixture, spreading it over the filling.

Bake at 425°F for 15 minutes. Then, reduce the oven temperature to 375°F and bake for another 40-45 minutes, until the top is golden brown and the filling is bubbling. If the edges brown too quickly, cover them with foil.

Let the bars cool before cutting into squares. Serve with whipped cream or ice cream if desired.