WET INGREDIENTS: Melt the butter in a large microwave-safe bowl. Let butter stand at room temperature for 5 minutes to cool down. (If the butter is hot, it will melt the sugars and cause greasy cookies.) Once the butter has cooled, add in the dark brown and light brown sugar. Whisk (or stir with a wooden spoon) until butter and sugars are well incorporated, about 1-2 minutes. Take your time to be sure the butter and sugar integrate; it will seem like they won't, but keep whisking until completely integrated. Add in the egg, vanilla, and molasses. Mix until combined.
DRY INGREDIENTS: Add in the baking soda, baking powder, and salt and mix to combine. Add the flour (See Note 2) on top. Mix until just combined, taking care not to overmix the dough. Add in the butterscotch chips and mix to incorporate. Cover the dough tightly and chill for 1 hour.
ROLL COOKIE DOUGH BALLS: Roll tall cylinders of dough. Each ball should be a full 1 and 1/2 tablespoons of dough (30 grams if you have a food scale). Cover and refrigerate the balls of dough for 5-10 more minutes (the dough gets warm when handled).
BAKE: Preheat the oven to 350 degrees F. Place dough balls on a parchment or Silpat-lined sheet pan (we like the Silpat sheet best for these cookies), spread far apart (I only bake 6-8 cookies at a time since they spread a lot), and bake for 9-14 minutes. Watch carefully, being sure not to overbake. (We remove ours at 10 minutes.) Slightly underbaked Butterscotch Cookies are the best! Remove from the oven and immediately, if needed, press any wayward edges of the cookie inwards with the back of a metal spatula. Let cookies stand on the cookie sheet for 4-5 minutes before removing them to a cooling rack.
STORAGE: Store cookies in an airtight container at room temperature. They're best enjoyed within 3-4 days. Freeze cookie dough as opposed to baked cookies (see next step).
FREEZING DOUGH: Instead of freezing the baked cookies, freeze the dough! Drop the cookie dough balls on a large sheet pan and freeze until solid. Once solid, transfer the frozen cookie dough balls to an airtight container or bag and freeze for up to 3 months. You can bake these cookies straight from the freezer. There is no need to thaw, but you may need to add a few extra minutes to the baking time. Bake until the edges are lightly browned, and the center is still soft.