Preheat the oven to 350 degrees. Heat 8 ounces semisweet chocolate chips and butter in a microwave-safe bowl in 20-second increments, stirring between each, until almost melted. Make sure not to over melt the chocolate, melt it just enough to mix – as I emphasized above in the post.
In a mixing bowl, beat eggs, brown sugar, and vanilla on high speed really well, until light and fluffy. Reduce speed to low; beat in melted chocolate (remember, the melted chocolate should not be too runny). Mix in flour mixture until just combined. Stir in chocolate chunks (or chocolate chips). If your batter is too runny (due to over melting the chocolate in step 1), let the batter stand for some time to get hard.
Spray baking sheets with cooking spray – it’s important: I found that these cookies really stick to the baking sheet if you skip this step. Drop tablespoons (or less) of dough onto cold baking sheets 2 inches apart. Let me emphasize – cold baking sheets (not hot or warm baking sheets that have been sitting underneath your pre-heated oven). Bake, rotating sheets halfway through, until cookies are shiny and crackly yet soft in centers, 12 to 15 minutes. Do not overcook the cookies, the texture should still be soft, that of a brownie, when you take them out of the oven. If you overcook them, they will be too hard. Do not bake them to a crisp, they are supposed to be soft.