Brown ground beef in a heavy skillet over medium heat; drain.
Reduce heat and add ketchup, onion and pickle relish if using. Heat through. Remove from heat.
Add shredded cheese and stir until cheese melts and mixture will hold together. Cool slightly.
Cover a 12-inch pizza pan or similar-sized round baking dish with aluminum foil.
Preheat oven to 350 degrees F.
Open and unroll crescent dough, laying out as in video on prepared baking pan.
Distribute ground beef mixture evenly over the solid part of the ring formed by the large end of the triangles, leaving about 1/4-inch of just dough on the inside circle to anchor points of triangle on (see video, it's hard to put into words)
Pull points of each triangle over the meat mixture, sealing on the bare part of the inner circle in the center.
Brush ring with egg yolk/egg white.
Bake at 350 degrees F for 25-30 minutes, or until crescent dough is golden brown.
For cheese sauce:
Cut Velveeta into 1-inch cubes and place in a small bowl. Add the butter, cover and microwave for 1 minute on HIGH. Remove and stir. Add cream and stir. Microwave for 20 seconds on HIGH, remove and stir until well blended.