From Chewy Gooey Crispy Crunchy Melt in Your Mouth Cookies, Alice Medrich 2010
1 1/3 cups unbleached all-purpose flour
1/2 teaspoon baking soda
10 tablespoons (1 1/4 sticks) unsalted butter, melted
1/2 cup quick cook rolled oats (or old-fashioned oats buzzed briefly in the processor to break them up a bit)
1/2 cup granulated sugar
1/4 cup packed dark brown sugar
2 tablespoons plus 1 teaspoon light corn syrup
2 tablespoons whole milk
1/2 teaspoon salt
7 ounces bittersweet or semisweet chocolate, chopped into chunks, or 1 heaping cup good chocolate chips
Whisk the flour and baking soda together in a small bowl. Set aside.
In a large bowl, whisk together the melted butter, oats, granulated and dark brown sugars, corn syrup, milk, and salt. Stir in the flour mixture. If the batter is still warm from the butter, let it cool to room temperature before adding the chocolate. Stir in the chocolate chunks/chips. Let the dough rest for at least several hours at room temperature or covered overnight in the fridge. (The resting time makes for an especially crisp and extra-flavorful cookie. If you refrigerate the dough, you may need to warm it to room temperature before you’re able to portion it into cookies.)
Preheat the oven to 325°F (163°C). Position the oven racks in the upper and lower thirds of the oven. (These cookies will not spread as they should in a convection oven, so make them only if you have a conventional oven.)
Place 3 large sheets of aluminum foil, cut to fit your baking sheets, on the counter. Divide the dough into 15 equal blobs of about 2 tablespoons each. Arrange 5 blobs of dough well apart on each sheet of foil, situating 4 in a square and 1 in the center. Flatten each piece of dough until it is about 3 1/2 inches in diameter. Slide two of the sheets of foil onto two baking sheets.
Bake for 20 to 25 minutes, until the cookies are thin and very brown, rotating the sheets from top to bottom and front to back halfway through the baking time to ensure even baking. If the finished cookies are too pale, they will not be crisp, although watch the cookies carefully as they turn brown quickly. Slide the cookies and foil onto wire racks to cool completely before removing the cookies from the foil. Repeat with the third batch—you can slide the last sheet of foil and cookie dough onto a hot baking sheet as long as you put the sheet in the oven immediately. Cool the cookies completely before stacking or storing. The cookies can be kept in an airtight container for at least 3 days.