In a saucepan, combine rhubarb and 3/4 cup sugar. Cover and cook over medium heat, stirring occasionally, until the rhubarb is tender, about 10 minutes., Pour into a greased 13x9-in. baking dish. In a bowl, combine flour, brown sugar, oats and remaining sugar. Cut in butter until crumbly; sprinkle over rhubarb. Bake at 400° for 30 minutes. , Meanwhile, in a saucepan, whisk the egg yolks and sugar; stir in cream. Cook and stir over low heat until a thermometer reads 160° and mixture thickens, 15-20 minutes. Remove from the heat; stir in vanilla. Serve warm over rhubarb crumble.