To make sure you get equal amounts of different ingredients in each frittata when making individual ones it's a good idea to keep your ‘wet’ ingredients separate from the other ingredients. Firstly, combine all your vegetables, cheese, herbs and other ‘solid’ ingredients and then divide this mixture evenly among muffin holes. Then whisk together your ‘wet’ ingredients such as eggs and milk and pour this into the muffin holes, dividing evenly. This way you won’t have a frittata that is all egg or all vegetables – basically they will be a more ‘balanced’ frittatas.