Start a campfire and wait until the flames die down and the coals glow red with white ash. Meanwhile, make the filling: In a large bowl, combine the peaches, blueberries, bourbon, sugar, cornstarch, cinnamon, lemon zest, lemon juice and vanilla. Mix well to coat the peaches and blueberries evenly. Set aside.
Make the topping: In a second large bowl, combine the flour, oats, sugar and salt. Add the cold butter cubes and cut the butter into the flour with a pastry blender, 2 knives or your hands. Mix until the texture is coarse and clumps in your palm when you squeeze a handful. Add the heavy cream and mix just until the dough comes together a bit more.
Pour the filling into a 12-inch cast-iron skillet or Dutch oven with a fitted lid and spread it out evenly. Spoon the topping mixture evenly over the filling, then cover with the lid. Place the skillet adjacent to the hot coals in a place where it will get a good amount of radiant heat so the topping cooks through evenly without burning. Use a metal shovel to pile hot coals on top of the lid (this will distribute heat from the top). Cook 45 to 50 minutes, rotating the skillet 90 degrees every 10 minutes so the cobbler cooks evenly. (Feed the fire with more wood as needed.) Change out the hot coals on top 2 or 3 times during cooking so the top stays hot throughout. When the cobbler is done, the fruit will be bubbling around the edges and the topping will be light and fluffy. Serve the cobbler straight from the pan with vanilla yogurt on the side.
You can also bake the cobbler, uncovered, in a 375 degrees F oven, 30 to 35 minutes.
Photograph from "Guy on Fire: 130 Recipes for Adventures in Outdoor Cooking"