In a medium mixing bowl, whisk together dry ingredients- flour, salt and chopped Rosemary. Set aside.
Using a mixer, cream butter and sugar until light and fluffy. Add egg yolks, vanilla and lemon zest. Mix until ingredients are combined. (Be careful not to over mix.)
Gradually add the dry ingredients to the wet ingredients while mixing. As the the ingredients first mix together, they will look like wet sand. When they come back together to form a soft dough, stop mixing.
Turn the cookie dough out of the mixing bowl onto a silicone baking mat or a large piece of parchment paper. Half the dough. Roll each half into 2 inch diameter logs without over handling the dough. Pat to create square ends, instead of tapered ends, on the logs to create uniform cookies when slicing.
Pour sparkling sugar on the parchment paper. Roll each log through the sugar to coat. When coated, roll each log in plastic wrap. Twist the ends to seal and freeze 1 hour-overnight.
When ready to bake, preheat oven to 350℉ & line 2 cookie sheets (or baking sheets) with parchment paper or silicone baking mats.
Remove cookie dough from freezer, slice into ½ inch thick, even slices. Place on baking sheets about 1 inch apart. Bake 14-16 minutes, or until the shortbread just starts to become golden brown around the edges. Be careful not to over bake.
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Notes
Spend a little extra to buy a high quality butter.
The same goes for eggs- splurge and buy the best ones you can.
You've bought a great butter, now don't over work it. When butter is beaten too long when creaming the butter and sugar together, it creates flat cookies.
Additionally, if the cookie dough is handled too much when forming it into logs, the butter in the dough will begin to melt. If at any point your dough starts to get sticky, refrigerate it until it firms back up.
Lastly, don't skimp on the chilling time. The colder + firmer your dough is when you bake it, the sharper and cleaner your edges will be. If the edges melt and spread out, the dough was not chilled long enough before baking.
If using freezer-proof plastic wrap, the cookie dough can last in the freezer for up to a month, allowing you to bake cookies from one log and have cookies later too!
“Nutrition facts” are calculated with an app and are an estimate at best. If you have special dietary needs, please use your own calculations or consult a physician for your health.