In a large mixing bowl, combine flour, salt, and sugar. Cut in cold butter until the mixture resembles coarse crumbs. Gradually add ice water, mixing gently until the dough holds together. Shape it into a disc, wrap tightly in plastic wrap, and refrigerate for 30 minutes.

While the crust chills, wash and slice the fresh strawberries and rhubarb. In a separate bowl, mix these fruits with sugar, cornstarch, vanilla extract, lemon juice, and salt. Let sit for 10-15 minutes to enhance flavor.

Preheat your oven to 425°F (220°C). Roll out the chilled crust to fit a 9-inch pie dish. Fit the rolled crust into the dish, trim excess, fill with strawberry-rhubarb mixture, and dot the top with cold butter.

Bake in the preheated oven for 15 minutes, then reduce temperature to 350°F (175°C) and continue baking for an additional 45-50 minutes until golden brown and bubbling.

Let the pie cool for at least 2 hours at room temperature to allow the filling to set before serving.