Rhubarb Crumble with Custard Sauce

8 cups chopped fresh or frozen rhubarb
1 1/4 cups granulated sugar, divided
2 1/2 cups all-purpose flour
1/4 cup packed brown sugar
1/4 cup quick-cooking oats
1 cup cold butter or margarine

In a saucepan, combine rhubarb and 3/4 cup of the sugar. Cover and cook over medium heat, stirring occasionally, until the rhubarb is tender, about 10 minutes. Pour into a greased 13 x 9-inch baking dish.

In a bowl, combine flour, brown sugar, oats and remaining sugar. Cut in butter until crumbly; sprinkle over rhubarb. Bake at 400 degrees F for 30 minutes. Meanwhile, prepare Custard Sauce.

Custard Sauce
6 egg yolks
1/2 cup granulated sugar
2 cups whipping cream
1 1/4 teaspoons vanilla extract

Whisk the egg yolks and sugar; stir in cream. Cook and stir over low heat until a candy thermometer reaches 160 degrees F and mixture thickens, about 15 to 20 minutes. Remove from the heat; stir in vanilla extract.

Serve warm over rhubarb crumble.

Yields 12 servings (2 1/2 cups sauce).