Place a heavy-bottomed saucepan over medium-low heat. Add the cubed butter to the pan and let it melt (cubing the butter first allows it to melt more evenly).

Once the butter is melted, it will start to foam. Stir frequently with a rubber spatula, scraping the bottom of the pan.

Continue to cook butter until you see brown specs in the butter and it has a nutty aroma.

Remove from heat immediately. Do not let it burn. Use the browned butter right away or put in the fridge for later use.

The key here is that after you brown the butter, you gotta let it cool. Completely. Back to room temperature, softened butter. I like to brown the butter the night before, pour it in a bowl and let it cool. Once it’s no longer warm, I wrap the bowl in plastic wrap and let it sit on the counter overnight. It’s back to good old softened butter that is ideal for cookie baking come morning.

BUT! You must must must scrape out those delicious brown bits when you mix up the batter. It’s key, I tell you.

Preheat oven to 300 degrees F. In a large mixing bowl, beat butter and shortening with an electric mixer on medium to high speed for 30 seconds. Add sugar, baking soda, cream of tartar, and salt. Beat mixture until combined, scraping sides of bowl occasionally. Beat in egg yolks and vanilla. Beat in as much of the flour as you can with the mixer. Stir in any remaining flour.

Shape dough into 1-inch balls. Place balls 2 inches apart on ungreased cookie sheets.

Bake in the preheated oven for 12 to 14 minutes or until edges are set; do not let edges brown. Cool cookies for 1 minute on cookie sheet. Transfer cookies to a wire rack and let cool.