• Get the sourdough discard out of the fridge about an hour before if you plan ahead, to let it come to room temperature
• Whisk the flour, salt, baking powder, baking soda and set aside
• I highly recommend using a scale to weigh the ingredients instead of using cup measurements, which is highly inaccurate

Brown the butter:

• This step is a must and you cannot skip it. Sourdough discard contains water and it is important that we remove water from the butter to reduce amount of liquid in the dough
• Melt the butter over medium-low heat and let it gradually melt. You will see large big bubbles and the butter is "foamy" at the beginning. Then the bubbles gets smaller and you start seeing brown bits appearing. Remove from the heat

Prepare the cookie dough:

• Add both brown and white sugar to the brown butter and stir. They don't have to melt. Let the mixture cool down for about 5 minutes or to at least warm before you add the egg yolk as we don't want to cook the yolk
• Add the yolk and sourdough discard and use a whisk to loosen the mixture and whisk until combined. Depending on your sourdough discard, some can be quite thick and some may be runny and mixed easily
• Sift the flour mixture you prepared earlier and use a spatula to fold to combine, but they are not entirely mixed yet, you still see some flour. Fold in the chopped nuts and chocolate chip morsels and fold to combine just until you don't see any more pockets of flour. Do not overmix. The dough is not an overly sticky type

Shape the cookies:

• 10 minutes before you plan to bake the cookies, preheat the oven to 415 F (210 C) for conventional oven, 395 F (195 C) for convection oven. Position the oven rack in the middle
• Line a large baking sheet with parchment paper. Get the cookie dough and divide into 4 equal portions, or you can weigh it. Each dough weigh roughly about 120 grams (4.23 oz). Round it up into a round tight ball so there won't be any "holes" in the cookies later
• Place it on a baking sheet, about 3 inches apart. Repeat with the other 4 cookie doughs

If you don't bake on the same day:

• If you don't want to bake right away, put them in the freezer to flash freeze for about 1 hour and then transfer to a freezer-friendly container or bag and the dough won't stick to each other
• When ready to bake, you can bake straight from the freezer without thawing. You may need to add 1-2 minutes extra at each baking temperature (there are two different baking temperatures)

Bake the cookies:

• Bake the cookies in a preheated oven for 6 mins. The cookies may not spread much yet at this point. Rotate the pan and lower temperature to 375 F (190 C) for conventional oven, 350 F (180 C) for convection oven. Bake for another 4 minutes. The cookies would have spreaded a bit but should be still tall and thick enough. Don't be tempted to bake it any longer
• Let the cookies cool on the baking pan for at least 10 minutes. The outer part of the cookies are "crusty" but the inside is heavenly "gooey".
• TIPS: If you find that the center of the cookies are too gooey to your liking, next time you know you can add a minute and see. Every oven is different, so you may have to experiment with baking time a bit. Vice versa, if the center is not gooey at all, then you may need to shorten the baking time or play with the baking temperature

Serve the cookies:

• The cookies have the best texture, crusty outside, gooey inside when served on the same day. The next day the cookie crust may have softened, but the inside should still be chewy, but may not be as gooey anymore. TIPS: I find that if I don't overbake them, the inside stay gooey even after 2 days.
• The cookies can be stored in air-tight container at room temperature for 3 days