Preheat oven to 425°F (220°C).

Make the crust: In a large bowl, combine flour, salt, and sugar. Cut in the cold butter until the mixture resembles coarse crumbs. Gradually add ice water, stirring until dough comes together. Divide dough in half, shape into discs, wrap in plastic, and refrigerate for at least 30 minutes.

Prepare the filling: In a bowl, mix together rhubarb, strawberries, sugar, cornstarch, lemon juice, cinnamon, and salt. Set aside.

Roll out one disc of dough and fit it into a 9-inch pie dish. Pour in the filling. Dot with butter cubes.

Roll out the second disc of dough and place it over the filling. Trim any excess dough, crimp edges, and make a few slits in the top for steam to escape.

Brush the top crust with heavy cream and sprinkle with coarse sugar.

Bake for 45–50 minutes, or until the crust is golden and the filling is bubbling. Let cool for at least 2 hours before slicing.