From the blog For Love of the Table
2 sticks (1/2 lb.) unsalted butter
1 t. vanilla
4 oz. (1 cup) walnuts, lightly toasted
1/4 c. light brown sugar (50 grams)
1/2 c. granulated sugar (100 grams)
1/2 t. salt
2 c. (8 oz.) all-purpose flour
2 oz. (1/2 cup) walnuts, toasted and very finely chopped
8 oz. semi-sweet chocolate
Melt the butter in a small, wide sauté pan set over medium heat. As the butter begins to sputter and pop, whisk occasionally. The butter solids will begin to turn brown. When the solids are golden brown and the butter has a pleasantly nutty aroma, transfer the butter to a heat proof container, or dip the bottom of the pan into a large bowl (or use the kitchen sink) of cool water to stop the cooking process. Set the butter aside and allow it to cool, stirring occasionally. When the butter has cooled, stir in the vanilla. Before proceeding with the recipe the butter should have cooled until it is opaque and thickened...but still liquid. If it solidifies, warm slightly.
In a food processor fitted with the metal blade, process the walnuts and the sugar until the walnuts are ground very finely. Pour in the butter—scraping the pan well. Process to combine. Scrape the sides of the bowl and add the flour and salt. Pulse until the flour is incorporated and the dough is clumpy. Transfer the clumps of dough onto a piece of plastic wrap and, using the plastic wrap, press into a thick disc. Wrap and refrigerate until firm—an hour or two.
Divide the dough into 6 equal portions. Working with 1 section at a time, and keeping the remainder of the dough refrigerated if the room is very warm, knead the dough between lightly floured hands until malleable. Roll the dough into a 10-inch sausage. Cut into 10 1-inch segments. Roll the segments into uniform balls. To form an acorn, place a ball on a teaspoon and using your thumb and index finger, shape the dough into an oval with a rounded point at the tip of the spoon. There should be a ridge formed by your thumb and index finger down the center of the rounded triangle of dough. Carefully remove the formed cookie from the spoon and place on a parchment lined sheet. Continue with the rest of the dough, spacing the formed cookies about an inch apart.
Bake the cookies for 14 to 16 minutes in a 325° oven until set and golden around the edges. Cool the cookies on the sheet for 10 minutes. Finish cooling on wire racks.
When the cookies are completely cool, melt the chocolate. Dip the wider end of the cookie in the chocolate and then in the finely ground walnuts. Place the decorated cookies on parchment lined sheets to allow the chocolate to set. Store in an air tight container. Makes 5 dozen cookies.
(Recipe adapted from Gourmet Magazine, December 2000)
http://www.forloveofthetable.com/2012/10/walnut-acorn-cookies.html