Preheat the oven to 350º F.
In a large bowl, add your gluten free flour and salt and whisk to blend.
Cut in the cold butter with a pastry blender.
Add the lemon juice, water, and one egg to a bowl and whisk. Add this to the flour-butter mixture and work with your hands into a dough ball.
Roll the dough on wax paper to ¼ inch thickness.
Cut up your plums and throw the pits away.
Put the plums in a bowl and add the sugar, lemon juice, and starch. Mix well.
Pour the plum mixture onto the flat crust.
Fold the edges up around the fruit.
Brush the crust with egg white.
Bake for 30 minutes.
Top with vanilla ice cream.