To make Churro Dough, in 2-quart saucepan, heat unsalted butter, 1 cup water and the salt to boiling. Add flour all at once; stir to combine. Cook, stirring constantly, until dough becomes a ball and no longer sticks to saucepan. Remove from heat; scrape dough into large bowl. Cool several minutes. (I use this time to crack the eggs and separate the one egg.) While mixture is still warm, beat in eggs and yolk, one at a time, until completely combined before adding the next. Fold in cooled apples.