Heat oven to 350 degrees F. Line the bottom AND up the sides of a 9-inch x 9-inch baking pan with parchment paper.
Beat together the butter, sugar, and vanilla in the bowl of a hand or stand mixer. Add the eggs one at a time, mixing well between each addition.
Stir together the flour, cocoa powder, and salt. Gradually add the dry ingredients to the butter mixture. Mix in the baking soda.
Mix in the chocolate chunks with a wooden spoon or spatula.
Pour the thick batter into the prepared dish and spread evenly.
Bake for 25 minutes, until brownies begin to pull away from the side of the pan. If you like your brownies less fudgy, add 5-7 minutes of additional baking time.