In a large, heavy saucepan over low heat, melt butter and chocolate. Melt chocolate, stirring occasionally, until smooth; remove from heat. Learn different techniques for How To Melt Chocolate.
Stir sugar into warm chocolate mixture. Stir in eggs, one at a time, beating well after each addition. Sift in flour, baking powder, and salt; stir until smooth. Stir in walnuts.
Cover and refrigerate, preferably for 1 1/2 hours; dough may be refrigerated longer or overnight, if you wish. This will be a soft dough and must be refrigerated. It may be left in saucepan or transferred to a bowl.
Freezing Dough: This dough freezes well. Make into the balls and freeze on a cookie sheet (before rolling in powdered sugar) and then store in Ziploc freezer bags. When ready to bake, remove as many balls as you need from the freezer and let thaw for 30 minutes; then roll in powdered sugar and bake.
Preheat oven to 300 degrees F.
Adjust two racks to divide oven into thirds. Line cookie sheets with parchment paper or use the Silicone Baking Mats (like photo on the right) to prevent the cookies from sticking.
In a small bowl, place powdered sugar. Sugar palms of your hands with some of the powdered sugar. Roll dough into 1 1/2-inch balls. Roll balls around in powdered sugar and place 2-inches apart onto prepared cookie sheets.
Bake 20 to 22 minutes or until tops of cookies are barely semi-firm to touch. DO NOT OVER BAKE - these should be slightly soft in the centers. (If you bake only one sheets at a time, bake high in oven.) Reverse position of sheets top to bottom and front to back once during baking to ensure even baking. Remove from oven and cool on wire cooling racks.
Storing: The cookies will keep in an airtight container for up to three days or in the freezer for up to two months. Sprinkle with fresh confectioners' sugar after thawing.
Yields 2 1/2 dozen cookies.
* For an extra rich chocolate cookie, substitute 65% to 70% dark chocolate for the unsweetened chocolate.
Chocolate Crinkle Cookies Recipe: https://whatscookingamerica.net/cookie/chocolateaggie.htm