Add flour and salt to a large bowl. Slice butter into ½-inch pieces and cut into flour with pastry cutter or with two knives until butter is pea-sized. 

Mix in ice water into flour/butter mixture just until no dry spots remain. Add a little more ice water if needed to make a soft dough. Be careful not to overwork the dough or crust will be tough. 

Wrap dough in plastic wrap and chill in the refrigerator for 30 minutes while preparing the filling.

In a large bowl add diced onions, turnips, carrots and potatoes and mix together to combine (see note). Add flour, chicken bouillon, salt, pepper, and cheese (if using) and stir well. Pour melted butter over mixture and stir to combine. Add chopped boneless skinless chicken and mix well.

Place an overturned baking sheet in the center of the oven. Preheat oven to 400 degrees F. Line a large baking sheet with parchment paper and set aside.

Dust a clean counter with flour. Divide the pasty dough into 6 balls. Roll out balls into 10-inch circles (they don't have to be perfectly round). 

Divide the chicken and vegetable filling evenly between pasties, placing about 1 cup of filling on lower half of each circle (leaving about a 1-inch border around the edge of the circle). Moisten the lower 1-inch border of dough using your fingers dipped in a little water. 

Fold the top half of the pasty down over the filling, pressing down to seal. Starting on one side, turn the edge over, forming a crimp. Repeat this process all along the edge to form a nice border. 

Place pasties on prepared baking sheet and taking a sharp knife, make a ¼-inch slit in the center of each pasty. Brush pasties lightly with evaporated milk (if desired, helps in the browning process).

Bake pasties at 400 degrees F for 20 minutes. Turn heat down to 375 degrees F and continue baking for 40 to 45 minutes or until pasties are brown and cooked through.