### Instructions:
1. Grease and line an 8×8 inch square baking pan with parchment paper, leaving an overhang on all sides for easy removal.
2. In a large, heavy-bottomed saucepan over medium-low heat, melt the butter and chopped dark chocolate together, stirring constantly until smooth and fully combined. Be careful not to scorch the chocolate.
3. Remove the pan from the heat and stir in the sweetened condensed milk, vanilla extract, and sea salt until completely incorporated and smooth.
4. Gently fold in the mashed raspberries. Be careful not to overmix, as you want pockets of raspberry flavor throughout.
5. Pour the fudge mixture into the prepared baking pan, spreading it evenly with a spatula.
6. If desired, sprinkle the dark chocolate chips over the top and gently swirl them into the fudge with a knife or skewer for a marbled effect.
7. Optionally, sprinkle with a pinch of flaky sea salt for a beautiful contrast in flavor and texture.
8. Refrigerate for at least 2-3 hours, or until thoroughly set.
9. Once set, use the parchment paper overhangs to lift the fudge out of the pan. Place it on a cutting board and cut into 1-inch squares.
10. Store the fudge in an airtight container in the refrigerator for up to 2 weeks.
### Short Tips:
* **Quality Matters:** Using high-quality dark chocolate makes a significant difference in the final taste and texture of your fudge.
* **Don’t Overcook:** Sweetened condensed milk fudge sets beautifully without needing to be boiled to a specific temperature. Overcooking can make it grainy.
* **Gentle Folding:** When adding the raspberries, be gentle to maintain their shape and prevent the fudge from becoming too watery.
* **Chill Completely:** Proper chilling is crucial for the fudge to set firmly and cut cleanly. Resist the urge to cut it too early!
* **Personalize It:** Feel free to experiment with other berries like blackberries or even a touch of raspberry liqueur for an extra boozy kick.
