A simple and comforting dessert featuring tender rhubarb folded into a custard‑topped yellow cake, quick to assemble and delicious warm or chilled.

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Preheat oven to 350 °F (175 °C). Grease a 9×13‑inch baking pan.
Prepare cake batter according to package directions. Pour batter into the pan and smooth the top.
In a bowl, toss chopped rhubarb with ¼ cup of the sugar; sprinkle evenly over the cake batter.
Combine remaining 1 cup sugar with the heavy cream; drizzle over the rhubarb layer.
Bake for 50–70 minutes, until the top is golden and the custard layer is set (a toothpick will come out mostly clean, though custardy underneath).
Cool for 10–15 minutes before serving warm with optional whipped topping, or refrigerate until chilled and slice cleanly.

Frozen rhubarb can be used—thaw and drain excess liquid before tossing with sugar.
Chilling the cake before slicing helps it hold shape.
Store covered in the refrigerator for up to 3–4 days.
Adjust sugar slightly if your rhubarb is very tart.