Portion calculator is missing when trying to use the Cooking and Alchemy tools. It will only add in one ingredient.

If this doesn’t help let me know and I will delete it. I believe you didn’t go far enough. It’s in the next step that you change the quantity for each ingredient you added to the cauldron. I selected all the ingredients from inventory I wanted.  Pushed Y to jump from inventory back to the cooking tool interface. Then there was an up down arrow for each ingredient to set the quantity.  

The UI for PC brings up a portion calculator when choosing ingredients. That’s why stated it was missing.