1-First Step: Preheat your oven to 350°F (175°C). Grease a 10-inch cast iron skillet with butter or oil spray. This prevents sticking and promotes crisp edges. Gather all ingredients for smooth workflow; melt butter in microwave for 1-2 minutes until liquid.

2-Second Step: In a large mixing bowl, whisk together 2 cups granulated sugar and 1 cup melted unsalted butter until smooth and glossy, about 1 minute. This base sets the sweet, shiny top characteristic of fudgy brownies.

3-Third Step: Add 4 large eggs one at a time, beating well after each. Stir in 1 tablespoon vanilla extract. The mixture should turn pale and creamy. Room-temp eggs incorporate air for lighter texture.

4-Fourth Step: Sift in 1 cup unsweetened cocoa powder, mixing until no lumps remain. Follow with 1.5 cups all-purpose flour and 1 teaspoon salt. Stir gently until just combined; overmixing toughens the brownie.

5-Fifth Step: Fold in 1 cup semi-sweet chocolate chips and optional 1/2 cup toffee bits. Pour half the batter into the prepared skillet, spreading evenly.

6-Sixth Step: Dollop 1/3 cup Nutella over the batter. Use a knife or skewer to swirl gently, creating marble patterns. Avoid over-swirling to keep distinct hazelnut pockets.

7-Seventh Step: Top with remaining batter, then dollop and swirl another 1/3 cup Nutella. Reserve 1/8 cup for post-bake drizzles if desired. Tap skillet on counter to release air bubbles.

8-Eighth Step: Bake at 350°F for 25-30 minutes. Edges set and pull from sides; center stays gooey with toothpick showing moist crumbs. Rotate halfway for even browning if your oven heats unevenly.

9-Final Step: Cool in skillet 10-15 minutes. The residual heat firms it up while keeping molten. Serve warm with vanilla ice cream, whipped cream, or fresh berries. Slice into wedges for sharing. Total time: 40 minutes. This easy nutella skillet brownie shines straight from the pan.