Crossed aldol reaction is a variation of aldol reaction.
crossed aldol reaction:
Step 1: The hydroxide ion deprotanates the enolizable aldehyde reversibly.
Step 2: Enolate ion 1 preferentially adds to the non-enolizable aldehyde, which has the sterically less hindered and, therefore, more accessible carbonyl carbon.
Step 3: Alkoxide ion 2 is protonated by water.
see also crossed aldol condensation