Warm, soft and saucy rhubarb on the bottom, topped with a light cake, with a crisp, caramelized sugar topping.
Set some water to boil for adding later in step 3.
Cover the bottom of an 8 or 9 inch square pan with the diced rhubarb.
In a medium bowl, mix together 1/2 - 3/4 cup sugar (depending on how sweet you like it or the sweetness of the fruit you are using), the butter, baking powder, salt, vanilla, milk and flour together. Spoon over fruit and spread to cover as much as possible. (There is not a ton of batter and it is thick-ish, but do try to cover the fruit as completely as possible, even if it seems quite a thin cover).
In a small bowl, stir together the remaining 3/4 cup white sugar and cornstarch. Sprinkle over the batter in pan. Pour boiling water over the top.
Place baking pan on top of a baking sheet (to catch any bubble overs). Bake at 375°F for 45 minutes (slightly longer is starting with frozen or partially frozen fruit, about 5-8 minutes longer). Allow to stand a few minutes, before enjoying warm as is, or with a scoop of vanilla ice cream.
You can use any fruit for this pudding cake. Strawberries, raspberries, blueberries, blackberries, peaches or plums would all work well.
Adjust the amount of sugar in both the cake batter and the topping depending on the fruit you are using. For rhubarb, I generally use 3/4 cup in the batter and 3/4 cup on top. You can reduce both anywhere down to about 1/2 cup, to taste.
Gluten free, 1-for-1 flour can be substituted.
Milk alternatives, such as almond milk can be used instead of regular milk. Vegan butter can be substitute for the butter, or substitute about 2 Tbsp coconut (or similar) oil for the butter.
Be sure to read the "Cook's Notes" included with this post, where I share some valuable tips, options, substitutions and variations for this recipe!