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 in a 9x13-inch baking pan; cover 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 and lay them shiny-side down.

Place a rack of spare ribs on each sheet, meaty-side up.

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.

Just before sealing completely, divide the beer mixture evenly into each packet.

Complete the seal.

Place the packets side-by-side on an 11x14-inch baking sheet.

Bake in the preheated oven until the ribs are very tender, 3 hours and 30 minutes to 4 hours.

Carefully open each packet, and drain the drippings into a saucepan.

You may only need the drippings from one packet.

Set ribs aside.

Simmer the drippings over medium-high heat until the sauce begins to thicken, about 5 minutes.

Brush the thickened sauce over the ribs.

Preheat the oven's broiler and set the oven rack about 6 inches from the heat source.

Place the ribs back into the oven and broil until the sauce is lightly caramelized, 5 to 7 minutes.