In a large bowl, combine the peaches, blueberries, bourbon, sugar, cornstarch, cinnamon, lemon zest, lemon juice and vanilla. Mix the ingredients well and to coat the peaches and blueberries and set aside.
In a second large bowl, make the topping by combining the flour, oats, sugar and salt. Now, add the cold butter squares and cut the butter into the flour with a food processor.
Pour the filling into a 12-inch cast-iron skillet (I used two 6-inch skillets), then spoon the topping mixture evenly over the filling.
Put your skillet onto a baking sheet to keep the oven clean and to catch any fruit that bubbles over (mine did). Bake the crumble uncovered at 375°F for 30 to 40 minutes or until the fruit is bubbling around the edges and the topping is golden in color.