Stir yeast into warm water to dissolve. In small bowl mix well the dissolved yeast, cream, milk and egg yolks; set aide. In a large bowl stir together flour, sugar and salt. Cut in 1/2 cup butter with pastry blender until mixture resembles coarse crumbs. Stir yeast mixture into flour mixture just to moisten. Spread dough with light film of butter to prevent drying, cover bowl with plastic and refrigerate overnight or up to 4 days. Shape and let rise, and bake into rolls, coffee cake or pastries.