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1. brown your butter. chop it up into chunks and place it in a saucepan on medium heat to melt. stir gently but continuously with a spoon or spatula as it heats up. it will begin to bubble as the water content starts boiling off, then start to foam up.

2. keep stirring, and turn the heat down a bit if it starts foaming too much. the trick is to keep an eye on the butter below the foam -- the color of the little yellow bits floating in the fat will start to change. add your rosemary to the saucepan now.

3. when it starts changing color it will get darker fast, so pay attention and don't let it burn. keep gently stirring until the butter smells caramely and looks nice golden brown. take it off the heat and pour the butter into a bowl so it doesn't keep cooking in the residual heat of the pan, making sure not to leave any milk solids behind. leave it to cool until it's comfortable to touch.

4. remove the sprig of rosemary from the butter and strip all the little leaves off into the butter. throw away the stick. add in the brown sugar, white sugar, sourdough discard, and egg yolk. beat for a few minutes with a whisk until light in color and fluffy.

5. in a different bowl, mix your flour, salt, baking powder, baking soda, and salt together until all evenly incorporated. this will let you mix it into the fluffy sugar-egg-butter mixture without beating all the air out of it.

6. gently mix the flour mixture into the wet mixture. try not to be too rough, but mix until everything is evenly incorporated.

7. add the chocolate chips and fold them in.

8. chill the cookie dough. the brown butter in the dough is currently melted, so if you try to bake them now, the butter will just come out of the dough and the cookies will be strange, flat, and greasy. you want it to chill until cold to the touch and kind of stiff.

9. preheat your oven to 375° F/ 190° C. while it preheats, put your cookies on a parchment-lined baking sheet. they'll be the prettiest shape if you make them cylinders standing on end instead of balls -- about twice as tall as they are wide. they'll melt downwards in the oven to have pretty folds, crispy edges, and a softer middle. this recipe makes 3 batches of 9 cookies when i make it. you can make them bigger or smaller, just remember to adjust your cooking time.