Prepare the Dough:

1. In a large bowl, mix flour and salt.
2. Add cold butter and mix with a pastry cutter or your fingers until the mixture resembles coarse crumbs.
3. Gradually add cold water, mixing until the dough comes together.
4. Knead briefly, wrap in plastic wrap, and refrigerate for at least 1 hour.

2. Make the Filling:

1. Combine diced rutabaga, onion, Yukon potatoes, parsley, sage, garlic powder, salt, and pepper in a bowl.
2. Stir well to evenly coat the vegetables with the seasoning.

3. Assemble the Pasties:

1. Preheat oven to 350°F and line a baking sheet with parchment paper.
2. Divide the dough into six equal portions and roll each into a circle about 1/8 inch thick.
3. Place a portion of the filling on one side of each circle.
4. Top each with 1 teaspoon of butter.
5. Fold the dough over the filling to create a half-moon shape. Crimp edges with a fork to seal.

4. Add Finishing Touches:

1. Brush the tops of the pasties with beaten egg for a golden crust.
2. Sprinkle lightly with salt, if desired.

5. Bake the Pasties:

1. Arrange the pasties on the prepared baking sheet.
2. Bake for 1 hour, or until the crust is golden brown and the filling is tender.
3. Allow to cool slightly before serving.