Preheat & Prep: Preheat oven to 350°F (175°C). Line an 8×8-inch baking pan with parchment paper, leaving a slight overhang for easy lifting later.
Bloom Espresso: In a small bowl, dissolve the instant espresso granules in the hot water.
Mix Wet Ingredients: In a medium bowl, whisk together melted butter, sugar, espresso mixture, eggs, and vanilla until smooth.
Combine Dry Ingredients: In a separate bowl, sift together flour, cocoa powder, (optional) confectioners’ sugar, and salt.
Form the Batter: Gently fold dry ingredients into the wet until just combined. Then fold in ½ cup chocolate chunks, reserving extra for topping.
Bake: Transfer batter to prepared pan, smooth the top, and sprinkle with reserved chocolate chunks.
Bake for 20–25 minutes, or until a toothpick inserted near the center comes out with a few moist crumbs not wet batter.
Cool & Slice: Let brownies cool completely in the pan. Use the parchment overhang to lift them out, then cut into 16 bars.
Store: Keep brownies in an airtight container. They can stay up to 3–4 days at room temperature and up to 1 week in the fridge. You can even store them in the freezer for up to 3 months.