Reddit reviews The Imbible: A Cocktail Guide for Beginning and Home Bartenders

Just speaking in totally basic, broad strokes:

Your typical cocktail will have a spirit, a sweet component, and a bitter/sour component to balance the sweet. The sour is usually citrus/acid in most cocktails, so we’ll nix that here (though as a substitution, maybe try to make a few shrubs and see if your friend is into the vinegar thing?) Bitters and Amaros are the obvious go-to from there, usually in stirred, more booze-forward cocktails, so I would go with that.

What you’re describing above when you mention milk and the like is called a ‘lengthener;’ these include low acid juices (OJ, Grapefruit) etc. and other low intensity liquids. They can add flavor/texture/volume to a drink, but IMO and to my taste usually aren’t enough to balance it much. For example, I don’t find the Brown Derby cocktail to be in balance (at least not iterations of it like this one). I find it too sweet, and I think it needs the addition of just a little bit of lemon/lime to keep the honey in check. The grapefruit, at least in low quantity, just doesn’t have enough acid on its own to balance the honey.

If you really wanna get into the workings of making your own cocktails using a ‘Mr. Potato Head’ approach with these components, I’d highly recommend picking up a copy of ‘The Imbible’ by Micah Lemon. He bases the structure of tons of drinks off of two examples (the Manhattan and the Daiquiri) and breaks it down in very easy terms for the reader. It’s also a very respectable guide to start learning technique and basics from; I would’ve loved to have that when I was starting out, it would’ve given me a huge leg up.