Preheat oven to 400ºF (200ºC). Line 2 baking sheets with parchment paper.
Pour the flour into a large bowl and add a pinch of salt. Cut the butter into slices, and put it into the bowl. Using your hands, rub the butter together with the flour until the floured butter is in the shape of small peas. Add the water, and mix the batter up until the dough is just moistened. Don’t overwork the dough. You’ll get a crumbly dough. If the dough looks a bit dry, add 2 more tablespoons of water. Pat the dough into a ball shape.
Prepare the filling by mixing the chicken, shallot, carrots, parsnips, and celery together. Make sure that the diced vegetables are cut pretty small, roughly 1/4-inch cubes. Take the rosemary and thyme and remove the leaves from the stem. Give it a couple rough chops. Mix the nutmeg, salt, rosemary, thyme, and pepper with the chicken and vegetables.
Divide the dough into 6 pieces. On a well-floured surface, use a floured rolling pin to roll out the dough to an 8 1/2 inch circle. As you are rolling out the dough, make sure to turn it frequently to prevent the dough from being stuck to the surface. You can prepare all the dough at once, or work one pasty at a time. I chose the latter because I didn’t have much counter space.
Take a small handful of filling and place it in the center of the rolled out dough. You want to make sure that there is about an inch of clear space around the edge of the dough. Brush the egg white along this empty space.
Fold the dough over the vegetables to create a semi-circle shape. Do this with confidence! Seal the pastry. You can crimp the edges with a fork or fold it like I did. When I folded the edges of the pasty, I brushed some egg along the edge so that the folds stayed put. Brush some of the egg wash over the entire pasty. Repeat these steps for the rest of the dough.
Place the prepared pasties on the baking sheets and bake for about 30 to 35 minutes, or until the pasties are golden brown.