• Preheat the oven to 350°F/ 180°C and line the baking dish with parchment paper.

Prepare the rhubarb:

• Chop rhubarb: Discard the leaves, wash and dry the stalks, and remove and discard the whitish lower ends. Cut the rhubarb into slices as thick as your finger.

  1 lb rhubarb
• Mix the rhubarb with sugar and place it in a colander.

  2 tablespoons granulated sugar
• Drain for about 30 minutes, then pat the pieces dry with paper towels.

Make the cake base:

• Wet ingredients: Beat sugar and soft butter in a large mixing bowl until fluffy, 4-5 minutes. Add the eggs, one at a time, beating for about 30 seconds after each addition. Add vanilla extract and a pinch of salt as well. Scrape the bowl with the rubber spatula a few times in between.

  1¼ cups granulated sugar + ¾ cup + 2 tablespoons unsalted butter + 4 large eggs + 1 teaspoon vanilla extract + a pinch of salt
• Dry ingredients: Mix flour and baking powder in a separate bowl.

  3 cups all-purpose flour + 2 teaspoons baking powder
• Combine: Add half of the flour mixture and mix it in shortly and at low speed. Next, add half of the milk and incorporate. Add the remaining flour, combine, add the remaining milk, and mix again on low speed.

  1 cup whole milk

Bake:

• Pour the batter into the prepared baking dish.
• Pat the rhubarb slices dry with paper towels and arrange them on top of the batter.
• Bake in the preheated oven for about 40 minutes.

Make the meringue:

• Make the meringue during the last 10 minutes of the cake’s baking time.
• Place the egg whites in a spotless mixing bowl and use very clean beaters to beat them (Note 4). Beat them on high speed until they begin to foam. Then, add salt and vinegar and continue beating until soft peaks start to form.

  4 egg whites + pinch of salt + 1 teaspoon vinegar
• Start adding the sugar gradually. Continue beating until the meringue is stiff and glossy (don’t overbeat it).

  ¾ cup granulated sugar

Finish baking:

• Spread the meringue evenly over the cake, and return the cake to the oven.
• Bake for another 10 to 15 minutes or until the meringue is golden (the exact time depends on your oven).
• Let the cake cool completely before you slice it.