Neither. Milk is an input for butter. One does not use milk on toast instead of butter which would make it a substitute. Nor does one always eat milk with butter which would make it a complement.
Milk and butter are complements.
complements
Relationship of good price to price of substitutes and complements: 1) Substitutes: as the price of substitutes for a good falls, the price of a good must fall in order to maintain demand. 2) Complements: as the price of complements falls, the price of a good can increase and still maintain the same level of demand.
Price of related goods fall into two categories: substitutes and complements. Complements are when a price decrease in one good increases the demand of another good. Substitutes are when a price decrease in one good decreases the demand for another good.
Prices of Related Goods (Substitutes and Complements) Changes in Income Preferences (Taste) Expectations Population (Number of Buyers)
Demand shifters include consumer income, number of consumer (population), consumer taste and preferences, and expectations: future prices of complements and substitutes and future income.
complements
Relationship of good price to price of substitutes and complements: 1) Substitutes: as the price of substitutes for a good falls, the price of a good must fall in order to maintain demand. 2) Complements: as the price of complements falls, the price of a good can increase and still maintain the same level of demand.
substitute
Price of related goods fall into two categories: substitutes and complements. Complements are when a price decrease in one good increases the demand of another good. Substitutes are when a price decrease in one good decreases the demand for another good.
You can try:I can't Believe it's not butter!Butter flavoured CriscoSmart Balance
butter milk
Prices of Related Goods (Substitutes and Complements) Changes in Income Preferences (Taste) Expectations Population (Number of Buyers)
Soy milk, almond milk, cashew milk, rice milk, oat milk, coconut milk, hemp milk.
Butter is made from milk, milk comes from cows.
Butter can not be made from dried milk.
actually it is made from butter and milk.
Milk your cow and get the milk from it. Then take the milk over to the butter machine and put the milk in.