Remove the shells from the oven and add them and the resulting juice into a large stock pot. (If using two baking dishes, place shells from one in the stock pot, then add vegetables before adding remaining shells)
Add all the cut vegetables, parsley, garlic, Bouquet Garni and pepper to the stock pot and mix together with shells.
Add the cold water, making sure to cover the shells by about 2 inches.
Place the stock pot over high heat and bring to a heavy boil.
Reduce heat to a high simmer, cover the pot and simmer for about 1 ½ hours, stirring occasionally to keep things mixed up.
Remove the cover and maintain a high simmer for 2 to 2 ½ hours until the liquid has reduced down to about half of original volume.
Turn off the heat and allow to cool so it will be easier to handle and the flavors continue to blend. Place a strainer or colander over a large bowl. Using a slotted spoon, place the solids into the strainer and allow to drain.
Continue this until all the solids have been removed from the stock pot.
Discard all the solids and return the drained stock back into the stockpot.
Place some cheese cloth in the strainer or colander, or use a very fine mesh strainer, and pour the liquid through to remove any remaining solids.
This can be used immediately or stored in the refrigerator for a couple of days.
If the stock will not be used within a couple of days, place the strained stock in freezer containers, label and freeze for put to six months.