An egg wash is a whole egg mixed with 1 tablespoon of water. An egg wash is commonly used on pastries to create a shiny golden-brown finish. Strictly speaking an egg wash is not necessary, but most professional pastry chefs and commercial bakeries use egg wash, and it is a way to improve the look of your baked goods.
There is a lot of history about Jews baking with Crisco rather than butter because vegetable shortening is parve, and functioned as a great substitute, resulting in light flaky pastries before the trans-fat police came along.
There were advertisements in hebrew
and even published a well-loved cookbook, Crisco Recipes for the Jewish Housewife.
So for the occasional holiday recipe The Food Jew says go for it.