You don’t spend time in USA “under an ESTA” — ESTA is an authorization to travel to the USA, and only for that. Once you’ve gotten there, you will be staying as a nonimmigrant alien admitted under the Visa Waiver Program. See this Question and Answer for more information.
An ESTA is generally valid for 2 years or until your passport expires, whichever comes first. It entitles you to fly to USA and ask to be let in as many times as you want in that period. Note that asking nicely to be let in is all the ESTA authorizes (it is like a US visa in that respect); whether you will actually be allowed in is up to the CBP agent, each time.
Making a second trip two months after an 11-day stay ended sounds completely unproblematic, unless there’s something other than what you have told us here that makes the CBP agent suspicious.
Credit:stackoverflow.com‘