For safekeeping, we froze leftover buttermilk into an ice cube tray. 14 cubes.
Now I need 2 cups of buttermilk.
Weigh a glass using my trusty triple beam balance. 280g
Add two random cubes. 340g
Add two more. 400g
So it looks like each cube is 30g
And by this table of buttermilk equivalent values it looks like 2 cups is 480g.
SO I need 480/30 cubes, or 16 cubes. I only got 14. Close enough.
Melt them in the measuring cup. 1-3/4 cups. Top it off with milk. Done.