Preheat a large saute pan (12-inch) over medium heat and add the diced bacon, cook, stirring often, until it has rendered its fat and become crisp. About 10 minutes. Transfer to a large plate or bowl and set aside.
Increase the heat to medium-high and cook 1/2 of the ground beef by smashing it into the pan with a spatula, and letting sear for 3 minutes. Add a pinch of salt, then break it up and cook, stirring often, until it still has some pink left in it, but isn't completely done. Transfer to the plate with the bacon. Repeat with the other half of the ground beef.
Add 1 tablespoon of oil (if necessary) and add the onions to the pan, along with a pinch of salt. Cook, stirring often, for 5 minutes, until it starts to become translucent. Add the remaining vegetables and cook, stirring often an additional 10 minutes. Deglaze with 1/2 cup of chicken broth, and cook until almost dry.
Add the tomato paste and flour and cook for an additional minute, stirring constantly.
Add the Shiner Bock beer and stir, scraping the bottom of the pan to remove any stuck-on bits. Bring to a simmer and cook until reduced by half. About 5 minutes.
Add the remaining chicken stock, the beef and bacon, and the rosemary and thyme. Stir thoroughly to make certain it's well combined. Bring to a simmer and cook, stirring occasionally, until the liquid has almost completely evaporated and the sauce is the consistency of gravy. About 30 minutes.
Potatoes and assembly
While the filling is simmering, preheat the oven to 375 degrees. Put the potatoes in a large pot and cover them by two inches with water. Bring to a boil, then reduce the heat to a rapid simmer, cover, and cook until a knife easily slides through the thickest potato. About 35 minutes. Drain and place back into the pot.
Put the half-and-half into a small saucepan and heat until the butter is completely melted. Pour into the potatoes, along with 1 tbsp. of kosher salt and 1 tsp. of freshly ground black pepper.
Mash the potatoes with a potato masher, skin and all, until your desired consistency.
Carefully dollop the top of the pie filling with all of the potatoes, then spread it with a spatula until the filling is completely covered.
Bake in the oven for 45 minutes. Serve.
If you don't have a large saute pan with metal handles, so you can transfer it from the stovetop to the oven, you'll need to spoon the filling into a 5 qt baking dish, then top with the potatoes prior to transferring to the oven.