Set your oven to 350 °F (175 °C). Line an 8×8-inch baking pan with parchment paper, letting 2-inch overhangs hang over the sides—this hack makes removal a breeze.

In a medium saucepan over low heat, gently melt the butter and chocolate chips together. Stir constantly with a rubber spatula until silky. Remove from heat before the last bits melt; carryover heat will finish the job.

Transfer the warm chocolate mixture to a mixing bowl. Add sugar and whisk until slightly thickened—this is where that shiny crust forms. Crack in the eggs, one at a time, beating well after each addition; stir in vanilla.

Sift in flour, cocoa powder, and salt over the wet mixture. Gently fold with a spatula—overworking will yield cakey brownies, and we want fudgy. Stir just until you see no streaks.

Dollop the Greek yogurt on top and use a butter knife to create gentle swirls—tiny pockets of creaminess that keep each bite tender.

Pour batter into the parchment-lined pan, smoothing the top. Bake for 22–26 minutes; start checking at 20 minutes if your oven runs hot. A toothpick inserted near the center should come out with moist crumbs—not raw batter.

Let brownies cool completely in the pan on a wire rack (30–40 minutes) for neat cuts. Lift them out using overhangs, place on a cutting board, and slice into 9 or 16 squares with a sharp knife wiped between cuts.