Preheat the oven to 375 degrees.

Add the egg whites to a mixing bowl, and beat until stiff peaks form.

Place the egg yolks, meat and butter into a blender or food processor, and pulse until well combined.

Combine half of the egg whites and the meat mixture into a bowl, and blend until combined.

Fold in the remaining egg whites.

Stir in the pork rind crumbs and add salt to taste if using.

Spread the mixture into a well greased loaf pan.

Bake for 80-90 minutes, or until crispy and browned on the outside and cooked through completely.

Drain off the excess grease, and allow the loaf to cool to room temperature before slicing to serve.