Mix brown sugar, oats, butter, cinnamon, and half of the flour together using a dough blender.
Press into pan - save about a cup or so- enough to sprinkle on the top before baking.
Combine cut up peaches and the rest of the flour (1/2 cup) and sprinkle over top
Combine white sugar, water, cornstarch, and vanilla in a saucepan. Heat until clear, about 5 minutes. Pour this mixture over the pan with the rest of the ingredients.
Sprinkle remaining crumble over the top
Bake for 1 hour or until lightly brown and bubbly. Enjoy!