Preheat oven to 350°F (175°C). Line an 8x8-inch pan with parchment paper and grease lightly.

Melt chopped chocolate and butter in a double boiler until smooth. Let cool slightly.

In a large bowl, vigorously whisk together eggs, granulated sugar, and brown sugar until pale and voluminous.

Fold the melted chocolate mixture and vanilla extract into the egg mixture until just combined.

Sift flour, cocoa powder, and salt over the batter. Fold gently until just a few streaks of flour remain.

Fold in the chopped walnuts evenly.

Pour batter into the pan. Bake 25-30 minutes until a toothpick comes out with moist crumbs. Cool before slicing.

To serve, place a warm brownie square on a plate, top with a scoop of vanilla ice cream, drizzle heavily with chocolate syrup, and sprinkle with chocolate chips.