Place 8 tablespoons (113 g) butter in a small saucepan and melt over medium heat. Once melted, crank up the heat to medium high. Stand by, continuously stirring and watching. Small golden brown bits (milk solids) will start to settle on the bottom of the pan. Once this happens, take it off the heat and pour into a large bowl (that is heat safe).(For more details on browning butter, check out my How to Perfectly Brown Butter tutorial) Add the sunflower seed oil, cold milk and vanilla to the browned butter. Add in the eggs, one at a time, make sure the first is well blended before adding the second. Whisk for about two minutes until slightly frothy. Add in the brown sugar, sugar, baking powder, baking soda and salt, whisking until well combined. Finally, whisk in the flour until completely blended. If the dough is still warm, let it sit for 10-15 minutes and then fold in the chocolate chips or chunks (otherwise they'll melt). The texture of the dough is a bit weird and the chocolate chips will sometimes resist combining with the dough. This is normal. Don’t sweat it.
Lay out some plastic wrap on the counter. Dump the cookie dough on top of the plastic and wrap tightly. Now shove the plastic-wrapped dough into the fridge and forget about it. I mean it. Go do something else. Let it hang out in there for at least 1 hour, ideally overnight.
When you’re ready to bake, preheat your oven to 375°F (190℃). Make sure you have a rack in the top third of the oven. Cover your baking sheets with either parchment paper or a silpat.
Roll 1 1/2 tablespoons of dough into a perfect like sphere. Place the dough balls on the covered baking sheet about 2 inches apart. Place in the freezer for 15 minutes. Take them directly from the freezer and onto that top rack in the oven and bake for 12-13 minutes or until golden brown around the edges. Once done baking, sprinkle with flaky sea salt (optional) and let cool completely on the baking sheet (no need to transfer to a wire rack).
Once they are cool, store them in an air-tight container. Also, gf cookies don’t last long. They get weird and dry. Fast. So unless you plan on eating all of them right away, I would consider freezing the dough balls completely and then placing them in a resealable freezer-safe plastic bag…that way you can bake them off fresh as you want to eat them.