How to make Items spawn when you combine two other items together

Question

My Idea is to have Two Herbs from the Player's Inventory and give them particular Item IDs like:

• 2 Combined Herbs give you a Potion of Health.
• 2 different Herb combinations give you a Potion of Nature.

...and so on.

So far, I can randomly spawn potions, but I need it to be specific like each Herb Combination gives me a specific assigned Potion.

This is a picture from the scene of potion making: