In a large bowl, use a rubber spatula to combine the sugars, butter, molasses, lemon zest, vanilla and egg until well blended. Stir in remaining ingredients (the dough will be stiff). Shape into a 15-inch-long log. Wrap with plastic wrap and refrigerate at least 3 hours. (see notes below for storing in the fridge)
Preheat the oven to 375℉.
Unwrap and cut into ¼-inch-thick slices. Arrange the slices 2-inches apart onto two ungreased baking sheets.
Bake one sheet at a time, 7 to 9 minutes or until the edges begin to brown. Cool for 1 to 2 minutes; remove the cookies from the baking sheet to a cooling rack. Repeat with the second baking sheet.
Onto completely cooled baking sheets, continue slicing and baking cookies.
Notes
Chill dough thoroughly before slicing
Slice evenly for consistent baking
The dough may be stored tightly wrapped in the refrigerator and sliced and baked as you'd like them. Keep the dough for no longer than one week in the refrigerator. Or to freeze, place the wrapped cookie dough log in the freezer until firm. Once the dough is firm, make sure the ends of plastic are twisted, and place the log in a large, resealable freezer bag. Freeze up to 1 month. To thaw, let dough stand 30 to 45 minutes at room temperature or until easy to cut into slices. Remove plastic, slice and continue as directed in recipe. Store baked cookies in a tightly covered container at room temperature for up to 5 days.