Alex Gooch of the BBC answered a question on the differences between 'made of' and 'made from.'
Gooch concluded that if you are referencing something that keep its form, you would use 'made of,' and if you were to reference something where the form is changed during the process of making, then you would use 'made from.'
Examples from the article for 'made of:'
- "The shirt is made of cotton." — 'Made of' is correctly used, as the shirt is still cotton - it didn't turn into polyester or anything not cotton in the process of making the shirt.
- "The house is made of bricks." — 'Made of' is correctly used, as the bricks used in making the walls of the house are still bricks. They didn't stop being bricks when they were carefully laid and set in the process of making the house.
Examples from the article for 'made from:'
- "Wine is made from grapes." — 'Made from' is correct in this instance, because when you pop open a bottle of wine and peer into the bottle, you don't see grapes, or crushed grapes, you see a liquid that is the result of fermenting the must (pulp) or juices of various types of grapes or fruits with naturally-occurring or added yeasts. The end product is no longer grapes, but a product that is made from grapes.
- "The paper is made from trees." — 'Made from' is correct in this instance, because when you look at a piece of paper, there is no longer any visible semblance of a tree with when you can point out. There is no bark, no grain, no leaves, sometimes nothing to indicate what species it could have been, especially if it was bleached. What the paper is, is a product created from the pulp of pulpwood logs and recycled paper products. Anything that was part of a tree (wood chips, logs, etc) stopped being part of a tree when it was pulped, and then turned into the final paper product.
Now, to the 'made with' consideration: 'Made with' implies that there are more than one important elements. 'Made with' is usually used when referencing ingredients, of which something like lemonade requires to become lemonade.
Examples for 'made with:'
- "The bagel is high in fiber because it is made with whole wheat flour." — 'Made with' is correct in this instance, because there wouldn't be bagels if the only ingredient used to make the bagel was whole wheat flour. The implication is that there are more, unspoken, and implied ingredients to reach the final product.
- "Our ice cream is made with real eggs and whole milk!" — 'Made with' is correct in this instance, because you can't just have ice cream made from just eggs and milk, you'd also need a sweetener and any applicable flavorings (such as vanilla or chocolate).
Now let's see if we can straighten out these sentences, and make them make sense:
'Made of' (something that retains its form):
"A lemonade is made of liquid."
You wouldn't accurately be able to say that the lemonade is made of lemons as you're only using the juices and pulps of a lemon, and generally discarding the lemons once you are done. However, a liquid with fruit bits and sugar in it becoming another liquid is still a liquid.
'Made from' (something that has its form changed in the process of making):
"My lemonade is made from lemons, water, and brown sugar."
If you take the juice of a lemon and pour it into a glass, you have a glass of lemon juice. If you take water, and pour it into a second glass, you have a glass of water. And if you take a spoonful of brown sugar and pour it into a third glass, you have a glass of brown sugar. But if you take all 3 ingredients, put it into a fourth glass, and stir, the ingredients will mix together and create a new and flavorful liquid that is the sum of its ingredients.
'Made with' (one of many important elements or ingredients):
"This lemonade is made with lemons from Florida!"
Considering that lemonade is made with more ingredients than just lemons (from Florida, or anywhere), you would rightly be able to assume that the lemons are only one of several important parts of the lemonade's recipe.
I hope this clears up your debate with your friend, and to put an exact answer to your question: You would say, "a lemonade is made with lemons."