Preheat your oven to 350°F (175°C) and line baking sheets with parchment paper.
In a bowl, whisk together the flour, baking soda, and salt. Set aside.
In another bowl, beat the softened butter and granulated sugar together with an electric mixer until light and fluffy, about 2-3 minutes.
Add the egg and vanilla extract to the butter mixture, and mix until well combined.
Gradually add the dry ingredients to the wet mixture, mixing until just combined.
Gently fold in the mashed raspberries, being careful not to overmix.
Using a cookie scoop or tablespoon, drop dough onto the prepared baking sheets, spacing them about 2 inches apart.
If desired, roll each ball of dough in additional granulated sugar for a sparkly finish.
Bake in the preheated oven for 10-12 minutes, or until the edges are slightly golden.
Remove from the oven and let the cookies cool on the baking sheet for 5 minutes before transferring them to a cooling rack to cool completely.