First combine both sugars and the slightly softened butter. Mix well in a bowl.
In a small separate bowl, whisk the egg. Then add the egg and vanilla to the butter and sugar mixture. Beat until thoroughly combined.
Add the sourdough starter to the wet ingredients and mix well.
In a separate bowl, combine all of the dry ingredients: the flour, salt, baking soda, and spices.
Add the dry ingredients into the wet ingredient bowl. Fold and stir until everything is just incorporated, but do not over mix!
Stir in the chocolate chips.
Chill dough in the refrigerator for at least one hour, or until the next day. Cove the bowl to prevent the dough from drying out. Allow dough that has chilled for several hours or longer to sit out at room temperature for about 30 to 60 minutes before dividing into individual cookies and baking.
Preheat the oven to 350F.
Scoop or pinch about 2 tablespoons of cookie dough and roughly form into balls (about golf ball size). Place them 2 to 3 inches apart on an un-greased baking sheet, or one lined with parchment paper.
Sprinkle a pinch of flaky sea salt on the top of each raw cookie before they go into the oven.
Bake for approximately 10 to 12 minutes*, or until the top has set and they turn golden brown. (See "bake time" notes below)
Allow the cookies to cool for several minutes on the baking pan, and then transfer them to a wire cooling rack.
Store leftovers at room temperature in an air-tight container for several days (up to a week), or freeze extras.