Preheat the oven to 425°F.
Wash the strawberries and drain them well.
Remove the stems and cut large berries in half, but leave small berries whole.
Cut the rhubarb stalks into 1/2 slices.
Combine the strawberries and rhubarb in a medium mixing bowl.In a small bowl, mix the sugar and cornstarch until lump free, then toss the mixture gently with the fruit.
Turn the mixture into a 9" x 5" loaf pan (or an 8" x 8" baking pan) and cover the pan with foil.
Set the pan on a baking sheet and bake for 15 to 20 minutes, or until the fruit filling begins to look translucent.
In a small mixing bowl, stir together the biscuit mix and milk to make a stiff dough (add a littde extra milk, if necessary).
Spoon the biscuit dough evenly over the filling.
Bake, uncovered, for 10 minutes, or until the biscuits are browned and cooked through.
Serve warm or at room temperature.