Mix the brown sugar, fajita seasoning, and paprika in a bowl.
Rub both sides of the spare ribs with the brown sugar mixture.
Place the spareribs on an 11 x 14 sheet pan. Cover the sheet pan tightly with heavy duty foil and refrigerate overnight.
Preheat an oven to 250 degrees F (120 degrees C).
Whisk together the beer, garlic, honey, Worcestershire sauce, and mustard in a bowl. Set aside.
Tear off 2 large sheets of heavy duty aluminum foil. Lay one sheet shiny-side down on a large sheet pan. Place one rack of spare ribs on a heet, meaty-side up.
Curl up the edges of the foil to create a bowl. Then repeat for the 2nd rack of ribs.
Divide the beer mixture evenly into each packet. Fold foil over the ribs to cover.
Tear off 2 more sheets of foil and place them on top of the ribs, shiny-side up.
Begin tightly folding the edges of the foil together to create a sealed packet. The two packets of ribs will fit nicely one one 11 x 14 sheet pan.
Bake until the ribs are tender, 3.5 to 4 hours. Don't cook them longer, as they will literally fall apart. I check them at the 3 hour mark. The meat is ready to come out of the oven when pierced with a fork you feel no resistance. Set ribs aside, removing and discarding the aluminum foil.
Carefully open one packet, and drain the drippings into a saucepan. Skim as much fat off the top as you can. Simmer the drippings over medium-high heat until the sauce begins to thicken, about 5 minutes.
place the ribs back onto the sheet pan. You can add a new sheet of aluminum foil or parchment paper for easy cleanup. Brush the thickened sauce over the ribs.
If you don't want to use the sauce from the cooked meat, and want a stickier rib, you can slather the ribs with your favorite bbq sauce.
Preheat the oven's broiler and set the oven rack about 6 inches from the heat source.
Broil until the sauce is lightly caramelized, 5 to 7 minutes. Watch them close so they don't burn.