Prepare a 9x9 (or 8x8) square baking pan. Line with a parchment paper, leaving some overhang on 2 sides. Set aside.
Transfer the freeze-dried raspberry into a small Ziploc bag. Crush them with a rolling pin. Take out 2 teaspoons crushed feezed-dried raspberry and put in a small bowl. Keep the rest in the Ziploc bag.
In a large pot over medium-high heat, add the cereal until they started to smell toasted, about 3 – 4 minutes, stirring frequently. Transfer to a large bowl to set aside. Keep the large pot on the stove (no heat).
In a light-colored small pot over medium heat, melt the butter, stirring occasionally. Once the butter has melted, it will start to bubble and foam, stirring occasionally. Soon milk solids (white spots) will appear at the bottom of the pan. Keep stirring. The butter and the milk solids will start to turn brown. It has a nutty aroma. Keep a close eye on the milk solids until they are just dark brown, but not black. The butter should be amber in color. This is brown butter.
Carefully transfer the butter to the large pot that was used. Turn on the heat to medium-low. Stir in the marshmallows. Cook until melted and smooth, stirring continuously. Stir in the salt.
Reduce the heat to low. Add the toasted cereal and stir gently for a few times. Remove from heat, working quickly to stir in crushed freeze-dried raspberry from the Ziploc bag and chocolate chips.
Transfer mixture to the prepared pan. Using a rubber spatula, gently spread mixture to fit the pan and gently press the mixture down into the pan. Do not press too hard.
Sprinkle the reserved freeze-dried raspberry and some chocolate chips over the top. Press down gently with the spatula, so the topping sticks to the treat. Set aside to cool for at least 1 hour or until the chocolate chips have set.
Use the parchment paper overhangs to lift the entire treat out of the pan. Place on a cutting board and cut into 9 big squares. Serve.