Heat olive oil in a large skillet over medium-high heat.
Add beef tips to the skillet in batches, searing until browned on all sides, about 3-4 minutes per batch. Remove beef tips and set aside.
In the same skillet, add diced onion and sliced mushrooms. Cook until softened and browned, about 6-8 minutes.
Add minced garlic and cook for 1 minute until fragrant.
Return the beef tips to the skillet. Pour in beef broth and Worcestershire sauce.
Add dried thyme, dried rosemary, salt, and black pepper. Stir to combine.
Bring the mixture to a simmer, then reduce heat to low. Cover and cook for 30 minutes, stirring occasionally.
In a small bowl, whisk together cornstarch and cold water until smooth.
Slowly pour the cornstarch mixture into the skillet while stirring. Cook for an additional 3-5 minutes until the gravy thickens.
Remove from heat and allow to cool completely.
Transfer the beef tips and gravy into a freezer-safe airtight container or heavy-duty freezer bag. Label with the date.
Freeze for up to 3 months.
To reheat, thaw overnight in the refrigerator and warm on the stove over medium heat until heated through.