Place roast beef into the insert of your slow cooker. In a 2-cup measuring cup, mix together all remaining ingredients. Pour over roast beef and set the timer for your slow cooker. (6-8 hours on Low)
Once roast beef has cooked, remove from slow cooker with tongs into a serving dish. Break apart lightly with two forks and then ladle about ¼ – ½ cup of gravy over roast beef.
Oven Method
Preheat oven to 250 degrees F. Place roast beef into a large roasting pan, heavy Dutch oven, or similar pan. In a 2-cup measuring cup, mix together all remaining ingredients. Pour over roast beef and cover with lid or tightly with aluminum foil.
Place in the oven and roast for 4-6 hours depending on cut of meat. Check at the 4 hour point to see if meat will easily pull apart when using two forks. If not, continue to roast, checking every half hour or so until meat easily pulls apart. Remove from the oven and allow to rest about five minutes. Pull meat apart, using two forks, and allow to rest in pan juices.
When ready to serve, remove meat to a serving dish with a slotted spoon. Then, ladle about 1/4 - 1/2 cup pan juices over meat for serving.
Notes
If you prefer a more pronounced flavor from the espresso and srirach, once the roast beef has been removed, use a fat separator on the gravy and then pour the gravy into a saucepan over medium heat. Simmer until the gravy has reduced by half. Add about 1 tablespoon each of espresso powder and sriracha sauce, if needed.