Can these be made ahead of time? Absolutely. The cupcakes can be baked 2 days ahead and stored, un-iced, layered with baking parchment in airtight containers. The frosting can be made 1 day ahead: cover with clingfilm and refrigerate; remove from fridge 1-2 hours before needed to allow to come to room temperature then beat briefly before using. Best iced and eaten on same day but iced cupcakes can be kept in fridge in airtight container for up to 1 day. Bring to room temperature before serving.
Can these be frozen? Un-iced cupcakes can be frozen, layered with baking parchment, in airtight containers for up to 2 months. Defrost for 3-4 hours on a wire rack at room temperature. Frosting can be frozen separately in airtight container for up to 3 months; defrost overnight in fridge then bring to room temperature and beat briefly before use.
No buttermilk? No problems, make you own using 250mL whole milk and adding 2 teaspoons of vinegar or lemon juice. Let it sit for five minutes to let it sour before using in your recipe.
Food colouring… what works best? The gel pastes give you the most vivid colour and can be purchased from cake supply stores on online. Americolor is my preferred gel paste brand because it’s allergy free unlike Wilton’s colours which contains egg, nut and shellfish traces depending on the colour. You can use supermarket colours like Queens (also nut and egg trace free).