Combine bittersweet chocolate chips and butter in a heatproof bowl. Melt over a pot of simmering water (double boiler) until smooth. Remove from heat and let cool slightly to lukewarm.

In a large bowl, whisk together eggs, granulated sugar, brown sugar, and vanilla extract until light and frothy. Gradually mix in the slightly cooled chocolate mixture until smooth.

In a separate bowl, sift together flour, cocoa powder, salt, and baking soda. Gradually fold the dry ingredients into the chocolate mixture using a spatula until just combined.

Gently fold in mini chocolate chips and chopped pecans (if using). Cover the bowl and refrigerate the dough for at least 30 minutes to firm up.

Preheat your oven to 350°F (175°C) and line baking sheets with parchment paper. Scoop rounded balls of dough onto the sheets, spacing 2 inches apart. Bake for 8-10 minutes, or until tops are cracked and centers are soft.

Let the cookies cool on the baking sheets for a few minutes before transferring to a wire rack. Serve warm or store in an airtight container for up to a week.