Before you begin, pop the raspberries in the freezer for about an hour. I put the entire container in there. Leave them in the freezer until you are ready to use them.
Preheat the oven to 350 degrees Fahrenheit.
Line a 9-inch baking pan with parchment paper, leaving a small overhang you can use to lift out the baked cake.
Sift the flour and cocoa powder into a large bowl. To do this, set a fine mesh sieve over the bowl. You can do the flour first and then the cocoa on top of it.
Gently whisk together the flour and cocoa powder. Set aside.
Melt the butter in a heat resistant container in the microwave, about 45 seconds. It doesn't have to be entirely melted.
Add the melted butter, packed brown sugar, and granulated sugar to the bowl of a stand mixer fitted with the paddle attachment and combine on low speed until well-blended and smooth.
Pour in the two eggs and beat until combined.
Add in the vanilla extract and mix briefly.
Slowly add in the dry ingredients. Mix on low speed until combined. Be sure to scrape down the sides and up from the bottom of the bowl to ensure all of the ingredients get evenly incorporated.
Remove the raspberries from the freezer and give them a large chop. Depending on the size, cutting them in half or into thirds is sufficient.
Add the chopped raspberries and 3/4 cup of mini chocolate chips to the cake batter. Use a wooden spoon or the spatula and mix gently until combined. Don't mix too aggressively or you will break down the raspberries further.
Pour the batter into the prepared pan and smooth out evenly with a small offset spatula or with the back of a tablespoon.
Sprinkle the top of the entire cake with 1/4 cup mini chocolate chips.
Place into the preheated oven and bake for about 35 minutes until a toothpick inserted into the center comes out relatively clean. Remember that if you put the toothpick into some melted chocolate chips, it will be wet, so try different spots. Basically, you don't want the whole cake to be gooey.
Let cool in the pan for about 15 minutes, then lift the brownies out using the parchment paper overhang. Place on a cutting board and let cool an additional 15 minutes. Use a sharp knife to cut into desired size.
Allow the cut brownies to cool completely on a wire rack.