There’s no mistaking a Levain cookie – a small mountain of fudgey, just-cooked dough filled with chocolate chunks that are miraculously suspended in a semi-molten state.
You could line up on West 74th Street for 45 minutes just to get one (worth it)
but it actually takes LESS TIME to make them at home!
(Also handy if you are not actually in New York.)

This recipe is for a half batch — about 10 fat cookies — and is easily doublable/double-and-a-halfable &c. &c. 
{ Recipe based on Kirbie Cravings, who did most of the legwork}

Gather:
1 1/4 cups + 2 tbsp plain flour (2 3/4 cups for a double batch)
1 tsp corn flour (aka. corn starch)
1/2 tsp baking soda
1/2 tsp salt

1/2 cup + 2 tbsp dark brown sugar (1 1/4 cup for a double batch)
1/4 cup white or caster sugar
1/2 cup (1 stick, or 112 g) cold butter — salted is best)
1 egg

1 cup large, good-quality milk chocolate chips or chunks (like Guittard or Ghirardelli)
1 cup walnut bits (or chopped whole walnuts)

Then:

1. Preheat the oven to 400ºF/205ºC.
2. Put the flour, corn flour, baking soda and salt in a medium-sized bowl, give it a quick stir with a fork and set aside.
3. Chop the butter and put it in the bowl of your stand mixer, along with the sugars.
4. Mix on medium speed until the mixture is smooth and pale (2–3 minutes).
5. Lower the speed as you add the egg.
6. Speed up again and mix until the egg is fully incorporated and the texture is smooth again. (It might take a while, since the butter is cold.)
7. Lower the speed to a slow stir, and gradually add the dry ingredients. (No need to be precious, just go as quickly as you can without sending flour everywhere.)
8. When the dry ingredients are incorporated, stop mixing and add in the chocolate chips and walnuts.
9. Stir with a wooden spoon until the bits are evenly distributed.
10. Spoon large tablespoons of dough onto a baking sheet. I don’t make these as huge as the Levain originals, but you want each one to be about a heaped 1/4 cup.
11. Bake for around 8 minutes — until the whole surface of each cookie is set/dry and the edges are starting to brown. You want them to still be soft and fudgey on the inside.
12. Continue in batches until you’re all done, transferring the finished cookies to a cooling rack as you go.
13. Try not to eat them all immediately (but don’t try too hard… they’re incredibly good when they’re still warm and gooey inside).