Open the recipe and tap the ✓ next to Ingredients, or tap Made It… at the top — if you don’t see it, tap More (•••) first. In Cook Mode it’s on the All done! page. Choose the Servings made and tap Made It. What the recipe used comes out of your pantry, and Undo shows for a moment in case you didn’t mean to. Servings beyond what’s planned for today are kept as leftovers, or all of them if nothing is planned. They show under the recipe’s name as Leftovers, and planning the recipe as Leftovers uses them up.

This only shows when Keep Count of What I Have is on in Settings → Keeping Count. If you check off every ingredient while cooking, the recipe offers to record it for you, unless you recorded it in the last four hours.