Take beef juices from pan and put into a saucepan. Use a little less than the amount you want of gravy. (example: if you wanted half a saucepan of gravy, use enough beef juices to get close to half since you'll be adding water.)

Once boiling, add some beef bouillon cubes for added flavor

Add a bit of hot or warm water to compensate for the added bouillon cubes.

Once at a boil, take a small cup and add a few teaspoons of the cornstarch and mix in a bit of water. Mix well until it is all combined. (This step is so you don't end up with lumps of cornstarch in your gravy.) Once mixed well, add to your gravy mixture.

Keep mixing with a wire whisk so nothing burns. Gravy will start to thicken shortly. If it's not thick enough for you, add more cornstarch by repeating the previous step.

When gravy is at desired thickness you're done! Take off heat and serve, enjoy!