Catalyzes the first step of the methylation pathway of phosphatidylcholine biosynthesis, the SAM-dependent methylation of phosphatidylethanolamine (PE) to phosphatidylmonomethylethanolamine (PMME). a 1,2-diacyl-sn-glycero-3-phosphoethanolamine + S-adenosyl-L-methionine = 1,2-diacyl-sn-glycero-3-phospho-N-methylethanolamine + H(+) + S-adenosyl-L-homocysteine Phospholipid metabolism; phosphatidylcholine biosynthesis. Belongs to the class VI-like SAM-binding methyltransferase superfamily. CHO2 family. Extended N-terminus.