Preheat and prep. Heat your oven to 350°F (175°C). Line an 8x8-inch (20x20 cm) metal baking pan with parchment, leaving a slight overhang for easy lifting. Lightly grease the parchment.

Warm the spread slightly. If your chocolate hazelnut protein spread is stiff, microwave it in a bowl for 15–20 seconds to make it easier to stir. You want it smooth and spreadable, not hot.

Mix the wet ingredients. In a large bowl, whisk together the chocolate hazelnut protein spread, brown sugar, eggs, oil, and vanilla until glossy and fully combined. This takes about 30–45 seconds of steady whisking.

Combine the dry ingredients. In a separate bowl, whisk flour, cocoa powder, baking powder, espresso powder, and salt. This helps prevent clumps and ensures even mixing.

Bring the batter together. Add the dry ingredients to the wet. Use a spatula to fold gently until just combined. Stop as soon as the flour disappears. Do not overmix or the brownies will turn cakey.

Add mix-ins. Fold in dark chocolate chips and chopped hazelnuts if using. Reserve a small handful to sprinkle on top for a pretty finish.

Pan and smooth. Scrape the batter into the lined pan. It will be thick. Spread it into an even layer with a spatula. Sprinkle the reserved chocolate and hazelnuts over the top.

Bake. Bake for 18–24 minutes, depending on your oven and pan. Look for set edges and a center that’s slightly soft. A toothpick should come out with moist crumbs, not wet batter.

Cool before slicing. Let the brownies cool in the pan on a rack for at least 30–45 minutes. Lift out using the parchment and cut into squares with a sharp knife. Wipe the knife between cuts for clean edges.

Finishing touch (optional). Sprinkle a pinch of flaky salt on top right after slicing to enhance the chocolate and hazelnut notes.