Preheat oven to 350°F (175°C)
Line pan with parchment, grease lightly
Toast hazelnuts until fragrant
Melt butter & chocolate in intervals, stir smooth
Whisk in sugar until glossy
Beat in eggs one at a time
Add vanilla & espresso powder
Fold in flour, cocoa & salt
Add toasted hazelnuts & chocolate chips
Swirl Nutella if using
Pour batter, spread evenly
Sprinkle hazelnuts on top
Bake 25–30 min, toothpick test
Cool completely before cutting