Mixing two types of apples gives you a nice sweet and sour taste to your palate.
I sometimes mix in some rum and brandy for customers who request for an adult version.
If using shortening or lard, cut down butter to 180 gm butter and 100 gm shortening/lard.
I have always used only butter in pie pastries because i love how light and buttery the pastry is. Here is a link on more about the science and test of using only butter versus using butter + shortening.