The correct answers are This cheese soufflé is incredibly hard to bake perfectly, The recipe is easy to mess up if you aren't careful, and It is impossible to whisk this heavy batter by hand.

Adjectives that describe how easy, difficult, or possible an action is (like hard, easy, impossible) are followed by a to-infinitive (to bake, to mess up, to whisk). We do not use the -ing form (gerund) after them in this structure.