Put cranberries, sugar, cornstarch, nutmeg, salt, and optional walnuts and orange liqueur in a large bowl. Mix well with a spoon and set aside.
Roll out bottom crust and place in pie plate and spoon cranberry filling into it. Dot top of filling with 1 tablespoon of Kerrygold Irish Butter broken into small pieces.
Roll out remaining dough disk and carefully lay top crust over filling. Trim excess dough, crimp edges of pie and cut some vents in top crust.
Separate egg white into a small bowl and fork beat with 1 tablespoon water. Brush crust with egg mixture and sprinkle with 1-2 teaspoons of sugar.
Bake on the middle rack of the oven until crust is just golden, about 40 minutes at 375 degrees F. Depending on your oven, it may take a little more time!
Note: Use a food processor to chop the cranberries quickly. I chop 3 cups of the cranberries and add 1 cup whole for a filling with varied texture.