Whisk together flour, sugar, and salt. Combine with butter until there is just 1/4-inch lumps of butter remaining.
Mix the egg and milk, and add it to the dough. Divide the dough in half. Shape each half into a 3" x 5" rectangle. Wrap in plastic and refrigerate for 30 minutes.
Remove from fridge and allow dough to rest for 15 to 20 minutes before you roll it out.
For the filling, heat 1 Tbsp butter in a saute pan over medium heat. Add apples and saute 5 minutes. Add Traeger Smoked Simple Syrup and cook 5 minutes more. Season with a pinch of salt and remove from heat.
Whisk together the brown sugar, flour, and cinnamon and combine with apples. Set aside.
Place one piece of the dough on a floured work surface and roll it into a rectangle about 1/8-inch thick and trim off the edges. Set aside. Roll the second piece of dough out the same as the first.
Beat the egg and brush it over the entire surface of the dough. Place a heaping tablespoon of filling into the center. Place the second sheet of dough over the first. Press firmly around each pocket of filling, sealing the dough on all sides. Press a fork around all edges.
Cut the dough evenly in between filling to make nine tarts. Press the cut edges with your fingers to seal, then with your fork again.
Place tarts on a lightly greased or parchment-lined baking sheet. Prick the top of each tart a few times with a fork. Refrigerate them, uncovered, for 30 minutes.
When ready to cook, start the Traeger according to grill isntructions. Set the temperature to 350 degrees F and preheat, lid closed, for 10 to 15 minutes.
Remove the tarts from the fridge and place in preheated grill for 30 to 35 minutes or until they're a light golden brown. When done, remove tarts from the grill and cool.
Combine powdered sugar and milk and drizzle over the top of cooled tarts. Enjoy!
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