You will need a dutch oven or stock pot and ramekins. Prepare your garlic, mushrooms, celery, and onions. Most likely your meat is already seasoned. If you are not using left overs, salt and pepper your meat.
Put some oil in a dutch oven or stock pot over medium heat. If you are NOT using leftover meat, this is the time you would brown your meat and then remove them to cook the vegetables. You would need to add more oil to cook your vegetables. If you ARE using leftover meat, use low-med heat add onions and saute them until they are soft and translucent. Add the garlic and saute for about 2 minutes longer. You may need to lower heat when you add garlic so it doesn't burn. It will depend on your stove.
Add celery and mushrooms to the pot and continue to saute for 2 more minutes.
Add Rosemary, Thyme, and tomato paste and stir. Add some salt and pepper to the vegetable mixture. Stir and cook about 30 more seconds.
Add meat back to the pot. Pour in the dry sherry and the 3 cups of water and Better then Bouillon low sodium beef bouillon. Stir and bring to a boil
Add the brown sugar and bay leaf. If you are NOT using leftover meat, cover the pot and simmer on low for 1 hour. If you ARE using leftover meat, cover and simmer on low for about 20 minutes and adding more water and bouillon if needed.
Depending if you are using fresh meat or leftovers, add potatoes after the above time of simmering. Continue to cover and simmer on low until potatoes can be penetrated by a fork easily. Depending on how big your chunks are could be 15-30 minutes. Check often.
Add the flour (be sure to dilute it first in water) to the stew/broth. Add the frozen vegetables and turn off the burner. Stir and taste to see if you need to add any more salt or pepper or water.
Once you like the consistency and taste, cover the pot and begin to prepare your ramekins. Preheat over to 400. Roll out puff pastry and cut out the dough to fit over the ramekin. Be sure to leave enough so you can press it down into the ramekin to meet the stew/broth and enough to press on to the ramekin's edge. Once you have cut out the tops get a ladle and stir the pot. Yes this time stirring the pot is ok lol. And begin to transfer the stew/broth into the ramekins filling it close to the top.
Place puff pastry dough on top of each ramekin and carefully pressing it down to meet the stew. Pinch it to the sides of the ramekin to prevent shrinking. Then take a sharp knife and put just a couple of slits in it to release the heat. Brush the pastry lightly with the egg wash. Place on a cookie sheet or jelly roll pan and place on bottom rack. It will be ready once the crust is golden brown. 15-25 minutes depending on your oven. Once it is done, let it sit for 10 min to cool down some. It will be very hot.