Chop mushrooms up. Chop them like you would pecans for a pecan pie. Place in large bowl.
Cut tenderloin up in 1/8” x 1/4” x 2” strips. The size is not exact just to illustrate how small to cut it. Toss them in with the mushrooms.
Toss in the beef.
Toss in all the mozzarella.
Toss in the whisked eggs.
Mix together well and divide into 6 even sized balls (approximately 8 oz each). Cover and let sit in refrigerator for 20 minutes.
Remove from refrigerator and pat out in patties and grill. Do not try to turn to quickly as they will fall apart.
I like to cook mine to a core temperature of 140 then let them rest covered for 20 minutes. Do not press or squeeze them, cook them either by timing or temperature. Squeezing them will dry them out and makes them tough.