Set your oven to 350°F (175°C). Preheating ensures that the cookies bake evenly.

In a bowl, whisk together the flour and kosher salt. This step helps distribute the salt evenly.

In a separate large bowl, combine the softened butter, brown sugar, and granulated sugar. Use an electric mixer to cream them together until fluffy, about 2-3 minutes. This process incorporates air, making your cookies light.

Mix in the vanilla extract, blending well to combine.

Gradually add the flour mixture into the creamed butter. Mix until just combined. Don’t overmix; it’s okay if some flour remains visible.

Gently fold in the bittersweet chocolate, chopped dark chocolate, and toasted hazelnuts. This ensures even distribution without breaking the chocolate.

Use a cookie scoop or two tablespoons to portion the dough onto a baking sheet lined with parchment paper. Leave enough space for the cookies to spread while baking.

Lightly sprinkle Maldon sea salt over the cookie dough balls before baking. This step enhances the flavors beautifully.

Place the baking sheet in the oven for 10–12 minutes, or until the cookies are golden around the edges but still soft in the center.

Allow the cookies to cool on the baking sheet for a few minutes before transferring them to a wire rack. Enjoy them warm or at room temperature.