Place 1 tablespoon of the butter into a 10 inch diameter cast iron and place the pan in the oven for 10 minutes.
Melt the remaining butter and set aside.
In a blender, pulse the flour, sugar, and salt to combine. Add the eggs, milk, vanilla, and melted butter. Process on high speed until batter is smooth and bubbly, about 30 seconds.
Remove the hot pan from the oven and pour the batter into the center of the pan.
Bake for 20 minutes without opening the oven to peek.
Dust the hot Dutch Baby with powdered sugar and cut into wedges. Serve with compote.
Making the Compote
In a medium saucepan combine the rhubarb, sugar, orange, and lemon juices. Cook over medium high heat for about 3 minutes or until the rhubarb is tender.
Add the strawberries and continue cooking for another 1-2 minutes or until the strawberries have become tender.
Raise the heat and continue cooking for a minute or so until the mixture has reduced a bit.