Salted Brown Butter Cookies

Ingredients

• 1 pound powdered sugar 
• 0.3 cup cornstarch 
• 1 large eggs 
• 2 cups flour all-purpose
• 1 teaspoon juice of lemon fresh
• 0.8 cup brown sugar light packed
• 4 teaspoons powdered egg whites such as just whites, or meringue powder (see cooks' notes) (not reconstituted)
• 0.8 teaspoon sea salt fine
• 0.8 cup butter unsalted cut into pieces
• 1 teaspoon vanilla 
• 0.3 cup water 

Equipment

• bowl
• frying pan
• baking sheet
• paper towels
• sauce pan
• baking paper
• oven
• whisk
• plastic wrap
• hand mixer
• stand mixer
• wax paper
• rolling pin

Directions

1. Melt butter in a 1- to 2-quart heavy saucepan over medium-low heat, then cook over low heat, swirling pan occasionally, until butter has a nutty aroma and is a rich brown color, and bottom of pan is speckled with browned bits of the milk solids, 8 to 10 minutes.
2. Transfer to a bowl, including browned milk solids on bottom, and chill until almost firm, about 30 minutes.
3. Whisk together flour and cornstarch in a bowl. Beat together butter and sugar in a large bowl with an electric mixer at medium-high speed until pale and fluffy, then beat in egg, salt, and vanilla.
4. Add flour mixture and mix on low speed until just combined well.
5. Form dough into 2 balls and flatten each into a 6-inch disk. Chill disks, wrapped in plastic wrap, until firmer, but not hard, 15 to 30 minutes.
6. Heat oven to 350°F with rack in middle position. Line a large baking sheet with parchment paper.
7. Roll out 1 disk of dough (keep remaining dough chilled) between 2 large sheets of wax paper 1/8 inch thick (this is when the rolling pin rings are really helpful). Freeze or chill dough on a baking sheet or tray until firm, 5 to 15 minutes, then cut out as many cookies as possible from dough.
8. Transfer cookies to lined baking sheet, arranging cookies about 1 inch apart. If the cookies become too warm to transfer, freeze or chill until firm (see Cooks' notes).
9. Bake cookies, 1 sheet at a time, until edges are golden, 8 to 10 minutes, then transfer to racks to cool completely.
10. Meanwhile, gather scraps of dough and repeat cookie process above. Parchment can be reused, but make sure baking sheet cools between batches. Make more cookies with remaining dough.
11. Beat together all ingredients in a large bowl with an electric mixer at medium speed until just combined, about 1 minute.
12. Increase speed to high and continue to beat until icing holds stiff peaks, about 3 minutes in a stand mixer or 10 minutes with a handheld. If not using icing immediately, cover surface with a dampened paper towel, then cover bowl with plastic wrap.
13. Transfer icing to a heavy-duty resealable bag and press out excess air. Snip a 1/8-inch opening in bottom corner of bag, then twist bag firmly just above icing and decoratively pipe icing onto cookies. If desired, sprinkle with sanding sugars or colorful sea salts while icing is still wet. (For tinted icing, see Cooks' notes.)
14. Let icing dry completely (about 1 hour) before storing cookies.
15. •Dough can be chilled up to 3 days.•
16. Rolling pin rings allow you to roll out your dough to an even thickness without bothering with rulers. And an evenly rolled-out dough makes for evenly baked cookies.•For the sharpest, cleanest edges, freeze or chill cut cookies until firm before baking.•Cookies keep, layered between sheets of wax paper or parchment, in a metal cookie tin at room temperature 1 week.•Meringue powder can be found in the baking section of large craft stores, such as Michael's, or on Amazon.com.•Icing can be made 1 day ahead and chilled, its surface covered with dampened paper towel and bowl covered with plastic wrap.•To tint icing, transfer 1/4 cup icing to a small bowl for each color and tint with food coloring. Spoon each color of icing into a resealable bag, pressing out excess air, and proceed as described above.