Step 3
With the paddle attachment, mix in granulated sugar, salt, egg yolk, 2 cups bread flour and pureed bananas. Switch mixer to a hook attachment, add 1 1/2 cups bread flour and sprinkle in cornstarch, then knead mixture on medium-low speed until a smooth and elastic dough forms (dough will be sticky). Cover the bowl with plastic wrap and allow to rise to until doubled in size, about 1 1/2 hours.