Prepare the Base

1. Preheat the oven to 325° and lightly grease an 8-inch square pan with butter or vegetable oil and line with parchment paper
2. In a small bowl, sift flour, baking soda and salt and set aside
3. Using an electric mixer on medium speed, cream butter, both sugars and vanilla, stopping the mixer twice to scrape the bowl with a rubber spatula
4. Add the egg and beat on medium speed until blended, about 10 seconds. Scrape the bowl
5. Add the dry ingredients and mix on low speed for 15 seconds. Scrape the bowl
6. Add the chocolate chips and blend until they are mixed in, 5-8 seconds
7. Spread the dough evenly over the bottom of the prepared pan with an offset spatula and set aside

1. Melt the chocolate and butter in the top of a double boiler placed over simmering water. Turn off the heat when almost melted and cover until fully melted, 5 minutes
2. Place the sugar in a medium-size mixing bowl and pour in the chocolate mixture. Using an electric mixer on medium speed, mix until blended, about 25 seconds. Scrape the bowl
3. With the mixer on medium-low speed, add the eggs and blend
4. Scrape the bowl after the eggs are added and blend until velvety, approximately 15 more seconds
5. Add the flour on low speed and mix for several seconds until blended
6. Pour the brownie batter evenly over the cookie base, place on the center rack of the oven and bake until the center has risen and a tester inserted in the center comes out with very moist crumbs, 35 minutes
7. Remove the pan from the oven and place it on a rack to cool for 25 minutes before cutting