Preheat oven to 350 degrees F. Line 9×9-in. pan with parchment paper, making sure parchment overlaps sides to create overhang for easy lifting.

Melt butter in microwave-safe bowl until fully melted.

Add brown sugar to large bowl. Pour melted butter and whisk immediately until mixture becomes thick and glossy.

Whisk in cocoa powder until smooth and well combined.

Add eggs and vanilla, whisking until mixture becomes fully blended.

Add flour and salt, stirring gently until combined (do not overmix).

Fold in chocolate chips.

Spread batter into prepared pan.

Bake for 18–20 minutes, until edges are set, center looks dry and toothpick inserted into center comes out clean.

In saucepan over medium heat, melt butter.

Add brown sugar, corn syrup and salt. Cook 1–2 minutes until bubbling.

Stir in heavy cream and cook for 1 more minute until slightly thickened.

Remove from heat and stir in vanilla and pecans.

Let mixture sit for 3–4 minutes to thicken slightly.

Spoon topping evenly over partially baked brownies and spread it gently with spatula.

Bake topped brownies at 350 degrees F for 20–25 minutes, until pecan layer is set at edges, top is glossy, center no longer looks runny, and toothpick inserted into center comes out mostly clean (a few moist crumbs are fine).

Cool brownies for at least 1 hour before slicing. For best results, refrigerate for 2–3 hours or overnight.