Preheat your oven to 350°F (175°C). Lightly grease a 9x13 inch baking pan and line it with parchment paper, leaving an overhang on the sides for easy lifting later. This makes cleanup a breeze!

In a large mixing bowl, melt the butter (you can do this in the microwave or on the stovetop). Add the granulated sugar to the melted butter and whisk well for about 1 minute until fully combined and slightly glossy. This helps create that crinkly top.

Whisk in the eggs, one at a time, making sure each is fully incorporated before adding the next. Stir in the vanilla extract. The mixture should be thick and smooth.

In a separate small bowl, whisk together the all-purpose flour, unsweetened cocoa powder, and salt. Gradually add the dry ingredients to the wet ingredients, folding gently with a rubber spatula until just combined. Be careful not to overmix, as this can lead to tough brownies.

Gently fold in the frozen raspberries and chocolate chips (if using) into the brownie batter. You want to distribute them without crushing the raspberries too much. A few smushed berries are fine and will add to the swirl effect!

Pour the batter evenly into your prepared baking pan. Bake for 28-32 minutes, or until a toothpick inserted into the center comes out with moist crumbs, but not wet batter. Remember, fudgy brownies are better slightly underbaked than overbaked!

Let the brownies cool completely in the pan on a wire rack before lifting them out using the parchment paper overhang. This is crucial for fudgy brownies that slice cleanly. Once cool, cut into squares and enjoy!