Preheat your oven to 350°F (177°C). Lightly grease your 9x13-inch baking pan or line it with parchment paper, leaving some overhang for easy removal later.
In a medium bowl, whisk together the all-purpose flour, baking soda, and salt until well combined. Set aside.
In a large bowl, use a hand mixer or stand mixer to beat the softened butter, light brown sugar, and granulated sugar until the mixture is light, fluffy, and creamy.
Beat in the eggs one at a time, ensuring each is fully incorporated before adding the next. Then mix in the vanilla extract.
Gradually add the flour mixture to the wet ingredients, mixing just until combined. Avoid overmixing.
Gently fold in the bittersweet chocolate chips and coarsely chopped mini pretzel twists, distributing them evenly throughout the dough.
Spread the dough evenly in your prepared baking pan, smoothing the top with a spatula. Bake for 25-30 minutes, until edges are golden and a toothpick inserted in center comes out with a few moist crumbs.
If desired, melt additional chocolate chips and/or peanut butter in microwave in 15-second bursts, stir, and drizzle over warm bars. Sprinkle crumbled pretzels on top.
Allow bars to cool completely in the pan on a wire rack before lifting out and slicing into squares or rectangles.