In a 10 ½ inch cast iron skillet* combine peach slices, blackberries, sugar, lemon juice, corn starch, vanilla, and cinnamon. Set aside.
Crush gingersnap cookies into small pieces. I did this by placing them in a resealable plastic baggie and crushing with a rubber mallet. Alternatively you could crush with a rolling-pin or pulse in a food processor.
Pour cookie pieces in to medium-sized bowl. Add brown sugar, flour, and oats and combine.
Using a pastry cutter (or knife and fork), cut cold butter into the mixture. Cut until mixture resembles coarse crumbs.
Spread crumb topping evenly over the fruit filling in the skillet.
Bake on 375F degrees for 30 minutes.
Allow crisp to cool slightly before serving, preferably topped with ice cream.
Notes
*I chose to make this crisp in a skillet. I believe that if you did not have a cast iron skillet an 8x8 pan would serve much the same.