Slow Cooker Sesame Beef and Broccoli

0 Optional Browning (this step improves the flavor and helps the beef to hold its shape as it cooks, but can be skipped in a pinch): Heat 2 Tbsp cooking oil (not in ingredients list) in a large skillet or saute pan over medium meat. Pat the beef dry and season it lightly with some salt and pepper. Add the beef to the skillet and cook on all sides until brown. It does not need to be cooked through since it will finish cooking in the slow cooker. 
2 Combine beef, ginger, garlic, stock, soy sauce, brown sugar, and rice vinegar in the bowl of a slow cooker. (Note: If you want to make this a freezer meal, combine all of these ingredients in a freezer-safe plastic bag or other container.)
4 Cook until beef is tender, low for 6 to 7 hours or high for 3 to 4 hours. (I prefer the low setting for the most tender beef.) After cooking, you can leave the slow cooker on the warm setting for up to 3 hours. 
6 When you’re about ready to serve, turn the slow cooker up to high. Whisk together the cornstarch, water, toasted sesame oil, and red pepper flakes (if using). Pour into the slow cooker and stir gently to combine. 
8 Cover the slow cooker and continue to cook for 15 minutes more. 
10 Meanwhile, steam the broccoli according to package instructions. 
12 Just before serving, stir the broccoli and green onions into the beef. (Stir gently as the beef is likely very tender and will have a tendency to break apart.) 
14 Top with sesame seeds. Serve over rice.