Preheat oven to 350F.
Slice all peaches and remove stone. Place into a bowl and add in brown sugar, corn starch, lemon juice, vanilla extract, cinnamon, salt, and nutmeg. Stir and pour into a 9x13 baking dish. Place dish into oven and bake for 15 minutes.
In a separate bowl, mix together the topping ingredients. Add flour, sugar, baking powder, salt, cubed or shredded butter, and milk. Using a fork or even your hands, mix together. It should be crumbly, but if you squeeze it together it should hold.
After peaches have baked for 15 minutes, remove from oven and then top with flour topping. I like to grab a handful, flatten it out and lay on top of the peaches. Repeat until the top is covered.
Brush on the egg wash and sprinkle the cinnamon sugar.
Place baking dish back into the oven for 50 minutes.
Remove and allow to cool slightly before topping with a scoop of vanilla ice cream.
