Acetic formic anhydride, $\mathrm{HCO}-\mathrm{O}-\mathrm{CO}-\mathrm{CH}{}_3$, reacts with 1 equiv of methylamine at low temperature. The main product is

The amine attacks the more electrophilic and less hindered formyl carbon (H instead of the electron-releasing, bulkier $\mathrm{CH}{}_3$). The acetate group is the leaving group, giving N-methylformamide and acetic acid.