Combine frozen blackberries, blueberries and raspberries in a large mixing bowl. Add brown sugar, lemon juice, lemon zest, vanilla and a little pinch of salt. Stir to fully coat fruit. Place fruit in a 10" cast iron skillet (or an 8x8 aluminum pan for grilling) or an 8x8 baking dish (if baking in oven). Let fruit sit in skillet and thaw while you make cobbler topping. Leave any accumulated juices from the thawing fruit in skillet. Set aside.
Make cobbler topping by mixing flour, sugar, baking powder and salt in a medium bowl. COLD butter is cut into the flour with a pastry blender (or a couple forks) until the butter is the size of peas. Once mixed, gently stir sour cream into the mixture (only until the dough begins to come together). Pinch dough into small pieces and place over the top of the fruit until covered. Sprinkle top of cobbler with raw sugar, if desired.
If baking in oven, preheat oven to 350°, then bake for 30-35 minutes or until top of cobbler is golden brown and juices are bubbling around the edges.
Start Traeger grill on the "Smoke" setting with the lid open for 4-5 minutes, or until the fire has been established and grill begins smoking. Turn temperature setting to 350° and preheat the grill for 10-15 minutes with the lid closed until temperature has been reached. Place cast iron skillet (or aluminum pan) directly onto the grill grate. Close lid, and cook the cobbler for 35 minutes at 350° (may take just a few minutes longer if you want the topping to be more golden brown in color). Cook until the dough topping is golden brown, and the juices are bubbling up around the edges of the cobbler.
Once cobbler is done, carefully remove skillet from grill or oven (remember the cast iron skillet will be very HOT). Let cobbler cool down for a few minutes, then scoop it up and serve warm, with a scoop of vanilla ice cream! ENJOY!
Traeger suggests using Apple or Pecan wood for this dessert. We ended up using Mesquite left over from cooking chicken and pork - no noticeable difference in taste!
Berry Cobbler (Traeger Grill Style) https://www.thegratefulgirlcooks.com/berry-cobbler-traeger-grill-style/