Place raspberries in a blender or food processor; process until smooth. Press raspberries with a spatula through a sieve over a bowl; discard seeds. Combine raspberry puree, rhubarb, and sugar in a medium saucepan; bring to a boil. Cover, reduce heat, and simmer 20 minutes. Uncover and cook until reduced to 2 1/2 cups (about 30 minutes), stirring occasionally. Remove from heat; stir in vanilla. Spoon into a bowl; cover and chill. Serve with toast and cheese.