Preheat your oven to 350°F then line a 9x5 inch loaf pan with parchment paper and set aside. .
In a medium bowl, cream together the butter, granulated sugar, and brown sugar until well combined.
¼ cup unsalted butter, ¼ cup packed brown sugar, 2 tablespoons granulated sugar
Add the egg yolk and vanilla extract, and mix until smooth.
1 large egg yolk, ½ teaspoon vanilla extract
Add the flour, baking soda, and salt, and stir until just combined. Fold in the chocolate chips or chunks.
⅔ cup all-purpose flour, ¼ teaspoon baking soda, ¼ teaspoon salt, ½ cup chocolate chunks
Press the dough into the prepared loaf pan, smoothing the top with a spatula. Top with more chocolate chunks.
Bake for 15-20 minutes, or until the edges are golden brown and a toothpick inserted into the center comes out clean.
Allow to cool in the pan for 10 minutes, then transfer to a wire rack to cool completely before slicing into bars.