Add the remaining sugar, egg, butter, salt, and 1 cup flour. With a dough hook or paddle attachment, mix/beat on low speed for 30 seconds, scrape down the sides of the bowl with a rubber spatula, then add the remaining flour. Beat on medium speed until the dough comes together and pulls away from the sides of the bowl, about 2 minutes. If the dough seems too wet to a point where kneading (next step) would be impossible, beat in more flour 1 Tablespoon at a time until you have a workable dough, similar to the photos above. Dough should be soft and a little sticky, but still manageable to knead with lightly floured hands.