Preheat oven to 350°F and grease a 9x13 baking dish.
Toss strawberries and rhubarb with 1/2 cup granulated sugar and let sit 10 minutes.
Layer half the bread cubes in the dish and spread the fruit mixture over them.
Add remaining bread cubes on top and press gently.
Whisk eggs, milk, cream, brown sugar, vanilla, cinnamon, and salt until smooth.
Pour custard evenly over the bread and press to soak.
Drizzle melted butter over the top.
Bake uncovered 45–50 minutes until set and golden.
Let rest 10 minutes before serving.