WETINGREDIENTS: Melt butter in a microwave-safe bowl, then cool to room temperature by refrigerating for 3-5 minutes. Transfer cooled butter to a large bowl. (Avoid hot butter as it can make cookies greasy.) Mix brown sugar until smooth, about 3 minutes. Add one whole egg, one egg yolk, molasses, and vanilla, stirring until smooth and combined.
DRYINGREDIENTS: Add cornstarch, salt, baking soda, baking powder, and cinnamon directly to wet ingredients and stir. Then, incorporate the flour (Note 2), mixing until just combined; mixture may appear dry initially but will integrate. Avoid over-mixing. If adding toffee bits, fold in gently. Cover dough securely and chill for 30 minutes.
CHILL: Take the dough out of the fridge and shape into tall, 40-gram balls (about 2 tablespoons each). Roll each ball in Demerara sugar placed in a small bowl. Arrange the sugared dough balls on a plate, cover, and refrigerate again for 45-60 minutes.
BAKE: Preheat oven to 325°F. Space dough balls on a lined sheet pan (6 per batch to prevent overcrowding) and bake for 9-14 minutes. Watch carefully, being sure to not over-bake. (We love these best at 12 minutes.) Let cookies cool on the sheet for 3-5 minutes before transferring to a cooling rack.
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Notes
Note 1: Molasses deepens the brown sugar flavor, but the cookies are still delicious without it.Note 2: Avoid overpacking the flour by spooning and leveling the flour.Note 3: Alternatively, roll the cookies in turbinado sugar or in sparkling sugar. As a last-resort option, the cookies can be rolled in plain white sugar.Nutritional information does not include the optional toffee chips.