Peel and rough chop veggies. Leave peeled garlic cloves whole.
Wrap fresh herbs into a sachet using cheesecloth and tie well.
Heat oven to 275°F.
Season meat with salt and pepper and heat up a heavy pot with a lid over medium heat using 1 tbsp vegetable oil.
Sear the meat in the pot and remove once it has been browned on all sides.
Add the other 1 tbsp vegetable oil and reduce the heat slightly.
Add the veggies and garlic and cook until translucent, stirring every minute or so.
Add the tomato paste, stir well and after 1 minute, deglaze the pan with the beer.
Add the brown sugar.
Let the beer reduce by half to concentrate the flavors.
Add the seared meat and pour the beef and chicken stocks.
Cover the pot with the lid and place it inside the oven.
Let it cook until the meat is tender and can be pulled apart with a fork. This can take anywhere from 1 1/2 hrs to 2 1/2 hrs, depending on your oven and the size of the meat (cut in pieces or a single chunk).
Once the meat is tender, take the pot out of the oven and turn it off.
Remove the meat from the pot and pull it apart using forks, aim for olive sized pieces, do not over do it.
Lightly brush pita bread with olive oil and place inside the oven for a quick warm up.
Assemble gyros and garnish with your favorite ingredients (ex. crumbled feta cheese, diced fresh tomatoes, red onions, olives, mixed greens, tzatziki etc).