Ethyl acetate is treated with excess $\mathrm{CH}{}_3\mathrm{MgBr}$ in dry ether followed by $\mathrm{H}{}_3\mathrm{O}{}^{+}$. The final organic product is

The first mole of Grignard adds and ethoxide leaves, giving acetone. Acetone is more reactive than the ester and adds a second mole of $\mathrm{CH}{}_3\mathrm{MgBr}$, giving $(\mathrm{CH}{}_3){}_3\mathrm{C}-\mathrm{OMgBr}$. Hydrolysis gives $(\mathrm{CH}{}_3){}_3\mathrm{C}-\mathrm{OH}$, 2-methylpropan-2-ol.