Recipe Rhubarb Upside-Down Cake

INGRÉDIENTS

1 1/2 cups sugar, divided
4 tablespoons unsalted butter, plus 1 stick and 6 tablespoons, cut into 1/2-inch cubes and chilled
Zest of 1 lemon
1 tablespoon plus 2 teaspoons fresh lemon juice
2 teaspoons vanilla extract
1/2 teaspoon kosher salt, divided
1 pound rhubarb, trimmed and cut into 1-inch pieces
2 1/2 cups all-purpose flour
2 teaspoons baking powder
1/3 cup whole milk
2 eggs lightly beaten
Ice cream or whipped cream for serving, optional

PRÉPARATION

Preheat the oven to 190°C.
Melt 250ml sugar, 4 tbsp butter, lemon zest and juice, vanilla, and 60ml salt in a 23cm cast-iron skillet over medium heat.
Once the butter and sugar have melted, add the rhubarb pieces and cook, stirring occasionally, until tender and lightly caramelized, 6 to 8 minutes depending on the thickness of the stalks.
Meanwhile, whisk the remaining sugar and salt, flour, and baking powder in a bowl. Add the remaining butter and, using your fingers, work it into the flour mixture to form coarse, pea-sized pieces. As Phyllis Grant would say, make it like you're snapping your fingers. Add the milk and eggs and mix until you have a soft, sticky dough. If your eggs are small, you may need a little extra milk to set the dough. Drop pieces of dough onto the warm rhubarb mixture, trying to cover the entire surface. It will feel like cobbler, but the dough will rise and fill any gaps. Bake on a baking sheet until golden brown and cooked through, about 30 to 35 minutes. Remove the pan from the oven and let the cake rest for about 10 minutes.
Place a large, flat serving platter over the skillet and quickly and carefully flip it over.
Serve warm or at room temperature with ice cream or whipped cream, if desired, but it's equally good plain.