We should all know about /u/ID10-T Simple Sugar Cookie recipe. Its simple and straight to the point! I wanted to take that and gear it more towards a "Cookies with milk" sorta zone.
Now bear with me here because I only did SLIGHT pre-planning for this recipe, but the idea has been stewing for a while now.

COOKIE:
Obviously Sugar Cookie (CAP) is the main star here when it comes to the cookie, but Vanilla Custard V1 (CAP) really helps bring in that rich sweet taste we long for in a sugar cookie! I personally wanted to lower the percentage of the sugar cookie from 8% (in the original recipe) to 6%, since I wanted the cookie to taste almost drowned out by some of the milk. (Since, if you have a cookie in milk, the cookie does tend to take a soggy/new flavor)

MILK:
This is where things get interesting. I found out in a different recipe (I may post it, but its not ready) that Bavarian Cream (TFA) and low percentages of Almond (FA) tend to make a REALLY delicious and rich milk. After a longer steep it may change the flavor profile slightly, but it really does take that milk up a notch! (Typically 3% bav cream and sub 1% almond does the trick). Also when paired with VERY low percentages of coconut extra (TFA) you can get an even richer/fresher milk.

Lastly, the Banana Cream (LA). This one was a odd ball. I've always been interested in low percentages of banana with a creamy base to add that little something extra to a recipe. I can hardly taste it, but I do think that it does help with the overall milky-ness of the flavor. Banana Cream is also a slightly sweet flavor, and that never hurts when your trying to get that sugar cookie profile.