Combine flour, sugar and salt in a large bowl. Cut in butter with pastry blender or two forks until mixture resembles coarse crumbs. Stir in undissolved yeast. Heat the cream and milk until very warm (120° to 130°F). Add egg yolks, mixing well. Add to flour mixture and stir just until dry ingredients are moistened. Spread light film of butter on dough to prevent drying. Cover bowl with plastic wrap and refrigerate overnight or up to 2 days.
Turn dough out onto a lightly floured surface and knead a few turns to shape into a ball. Roll the dough into a 12 x 16-inch rectangle. Spread with softened butter. Combine brown sugar and cinnamon and sprinkle over butter, followed by toffee chips and pecans. Roll up jellyroll style and pinch seams to seal. Cut roll into 15 equal slices. Arrange cut side up, in a greased 13 x 9-inch pan.
Let rolls rise in a warm place until nearly double, about 1 hour. Bake in preheated 350°F oven for 30 to 35 minutes or until light brown. If rolls are browning too quickly, cover lightly with a piece of foil for the last 5 to 10 minutes of baking.
Remove rolls from oven and let cool a few minutes before removing from pan. Cool 10 minutes and frost.
To make caramel icing, melt butter in small saucepan. Add brown sugar and cook, stirring constantly, until mixture just comes to a boil. Remove from heat; stir in milk. Add powdered sugar and vanilla, beating until smooth. Drizzle warm icing over rolls.
Recipe Tip: Use the residue of butter on the butter wrapper to coat top of dough.