Set out eggs to bring to room temperature.
Melt butter and chocolate in small sauce pan over low heat, stirring occasionally until smooth. This should take 6-8 minutes. Let cool another five minutes while mixing dry ingredients and chopping the nuts
Whisk together 1 C of the flour, the granulated sugar, baking powder, and salt into a large mixing bowl. Add eggs and vanilla extract. If you're using a stand mixture--like me--then be sure to use the whisk attachment at medium to high speed. Do not use the paddle in this step. The idea is to inject air into the eggs so you don't get flat cookies, so whisk the egg/flour/sugar mixture for 4-5 minutes before adding the chocolate in the next step.
When butter/chocolate mixture is cool, add to bowl with the eggs/flour/sugar. Whisk on low-to-medium speed, scraping the side of the bowl as needed, until well blended. This will probably take 2-3 minutes more.
Add the remaining flour and the nuts. Stir with a wooden spoon until blended. You can also use the paddle at low speed on your stand mixture for this step.
Cover with plastic wrap and refrigerate for about an hour.
Preheat oven to 300 degrees. Put the powdered sugar in a shallow bowl and line cookie sheets with silicon mats or parchment paper.
Form cookie dough into 1.25 inch balls. Roll the balls in the powdered sugar and place 2 inches apart on the cookie sheets. Use powdered sugar on your fingertips to keep the dough from sticking to them.
Bake 15-18 minutes until set. Cookies will flatten while baking. I found 15 minutes was exactly right in my oven to get a cookie with a chewy middle and crisp outside.
Let the cookies cool on the cookie sheet for at least fifteen minutes after you take them out of the oven. When they first come out of the oven they will be fragile, but will firm up nicely as they cool. They will also flatten slightly as they cool. If they turn into flat little pancakes, you probably didn't whisk the eggs/flour/sugar mixture sufficiently.
