Preheat oven to 350°F and place pie crust in a 9-inch pie dish. Set on a baking sheet.
Spread rhubarb and strawberries evenly inside the crust.
Whisk eggs, sugar, flour, milk, and nutmeg in a bowl until smooth. Pour over fruit.
Dot with butter and gently tap the pie plate to settle the filling.
Bake for 55–65 minutes, or until custard is fully set. Rotate halfway through.
Optional: Warm jam and water, then brush on top for a glossy finish.
Cool to room temperature, then chill for at least 1 hour before slicing.