Pat chuck roast dry with paper towel and season with salt and pepper.

In large skillet set over medium-high heat, heat oil. Sear chuck roast, flipping once, for 4 to 6 minutes or until golden brown; using tongs, transfer to plate. Let cool slightly and cut into 2-inch chunks.

Meanwhile, halve onion. Slice 1 half onion crosswise into 4 slices. Dice remaining half onion and reserve for Step 10.

Transfer onion slices, carrot and garlic to skillet over medium heat. Cook, stirring occasionally, for 4 to 5 minutes or until starting to brown. Stir in 1 cup beef stock. Add ancho pepper, chile de arbol and guajillo pepper; bring to a boil. Reduce heat to medium-low. Simmer, stirring occasionally, for 20 minutes or until chilies are softened. Let mixture cool slightly; transfer mixture to blender and blend until smooth.

Pass sauce through fine-mesh sieve into Dutch oven set over medium-high heat (discard solids). Stir in remaining beef stock, beef, thyme and cinnamon; bring to a boil. Reduce heat to medium-low; simmer, stirring occasionally, for 2 ½ to 3 hours or until beef is very tender.

Transfer beef to large bowl. Using 2 forks, shred beef and return beef and accumulated juices to Dutch oven; stir to coat.

Preheat broiler.

Transfer beef mixture to broil-safe skillet, spreading in even layer. Sprinkle with Oaxaca cheese.

Broil for 2 to 3 minutes or until cheese is melted and golden.

Divide cheesy beef birria among 6 bags of FRITOS^® Original Corn Chips. Drizzle with sour cream. Top with reserved diced onion, cilantro and chilies.