COMBINE AND MELT: In a medium pot, melt butter over medium heat. Add sugars. Remove from heat and stir until mixture is smooth, about 2 minutes. Let cool on stove or put in fridge to cool for 5 minutes.
ADD LIQUID: Stir in egg, egg yolk and vanilla.
ADD DRY INGREDIENTS: Use a wooden spoon to fold in flour, salt and baking soda just until combined. Fold in chocolate chips/chunks - make sure mixture is cool first so chocolate doesn't melt - I use my hands to distribute chocolate chips evenly.
CHILL DOUGH: Wrap dough in plastic to firm it up in the fridge for at least 30 minutes. To bring out the toffee flavor more, chill dough for 24-36 hours. (NOTE: cookies can be baked without chilling if you're in a rush, but they may spread more in the oven and flavor will not be as deep).
Preheat oven to 325F.
BAKE: Cut chilled dough into thick slices for easier handling. Form into cookie mounds of 1 1/2 to 2 inches and place on baking sheets lined with parchment paper. [At this point, the mounds can be frozen and put into ziploc bags to be baked as you need them]. Bake for 12-14 minutes until golden brown. Remove cookies from oven and sprinkle lightly with sea salt.
COOL: Cool cookies for 5 minutes before transferring them to a cooling rack or a plate.