Roll out 1 package of the crescent rolls into a 9x13" baking dish. Press seams together.
Combine cream cheese, brown sugar, vanilla, lemon juice & egg yolk & spread over crescent rolls in baking dish. Roll out second package of crescent rolls over cheese mixture. Do not seal these seams. Brush with reserved egg white.
Combine chopped nuts and brown sugar. Sprinkle on top of coffee cake. Bake in a pre-heated 350 degree oven for 35-40 minutes. Let cool completely before cutting.