Prepare the beef: Slice the beef into thin strips against the grain. Try to keep the strips as uniform as possible for even drying.

Make the marinade: In a medium-sized bowl, combine Dr. Pepper, soy sauce, Worcestershire sauce, brown sugar, honey, garlic, black pepper, smoked paprika, onion powder, cumin, and red pepper flakes (if using). Stir well until the sugar dissolves.

Marinate the beef: Add the beef strips to the marinade, along with the sliced jalapeños. Toss to ensure all the beef is coated. Cover the bowl and refrigerate for at least 4 hours, or overnight for a more intense flavor.

Preheat your dehydrator or oven: If using a dehydrator, set it to 160°F (71°C). If using an oven, preheat it to the lowest possible setting (usually around 170°F or 75°C).

Dehydrate the beef: Remove the beef from the marinade, letting any excess liquid drip off. Arrange the strips in a single layer on the dehydrator trays or a baking sheet lined with parchment paper (if using the oven). Avoid overlapping the strips.

Dry the jerky: In a dehydrator, dry the jerky for 4-6 hours. If using an oven, prop the oven door open slightly to allow moisture to escape and dry the jerky for 4-6 hours, checking occasionally.

Check for doneness: The jerky is done when it is firm, but still slightly pliable (not brittle). If you bend a piece, it should crack but not break completely.

Cool and store: Let the jerky cool completely before storing it in an airtight container or vacuum-sealed bag.