• Start a large pot of boiling water and cook rice noodles according to instructions on the package. Watch carefully, because they cook quickly. Remove noodles and place in a colander. Drain and rinse continuously with cold water for 2 to 3 minutes. Shake the colander several times to drain the water. Place on a large plate and set aside and allow the noodles to dry.
• Prep and clean the lettuce, cilantro and jalapenos.
• Prep the onion, pepper, lemongrass and the garlic.
• Slice the beef and place in a large bowl along with the lemongrass, garlic, oyster sauce and sesame oil. Marinate the beef for at least 15 minutes and up to a few hours in the refrigerator.
• Heat a 9-inch nonstick skillet at medium-high and add 1/2 to 1 tablespoon butter. Allow the butter to melt and add beef  with 1/2 to 1 Tbsp of butter. Cook beef (& shrimp) along with a little bit of peppers and onions in small batches, about 3 to 4 minutes on each side, or until cooked through and browned. Repeat until you have cooked all of the meat. (You may need to wipe the skillet clean in between batches so you don't burn the beef.)
• Roll into spring rolls with rice noodles, lettuce and cilantro along with the beef and shrimp (if using). Serve immediately.

Tips:

• Be sure to not overfill the skillet, cook the beef in batches. If you overfill, the meat will not brown quickly and you will have overcooked your beef and make it tougher.
• Always, watch the noodles very carefully, they cook very fast in some cases in just 3 minutes! Drain in a colander and drain. You definitely want to drain and rinse with cold water because you do not want them to stick together. Allow them to cool and I like to warm them up in the microwave for about 30-45 seconds before adding them to the rice paper.
• If you want to do shrimp as well, marinate in a separate container from the beef. I often stir fry it along with the beef unless someone does not eat beef or is allergic to shellfish.