Preheat your oven to 350°F (175°C). Line a 9-inch square metal baking pan with parchment paper, making sure to leave a 2-inch overhang on two sides; this will make lifting easy!
In a large mixing bowl, gently melt the butter. Whisk in the granulated sugar, brown sugar, and oil until the mixture looks glossy and smooth, which takes about 30 to 60 seconds.
Beat in the large eggs, one at a time, whisking well after each addition until they are fully combined. Stir in the pure vanilla extract and espresso powder (if you're using it) until the mixture looks wonderfully thick and shiny.
In a separate, medium-sized bowl, quickly whisk together the flour, cocoa powder, and salt.
Sprinkle the dry ingredient mixture over your wet ingredients. Using a rubber spatula, gently fold everything together until just combined and you no longer see any dry streaks of flour. Be careful not to overmix!
Fold in your chocolate chips. Spread the batter evenly into your prepared pan and smooth the top. Bake for 24 to 28 minutes, or until a toothpick inserted into the center comes out with mostly damp crumbs (no wet batter).
Let the brownies cool completely in the pan for 20 to 30 minutes. Then, use the parchment paper overhang to carefully lift the entire brownie slab out onto a cutting board. For the neatest heart shapes, pop the slab into the fridge for an extra 15 to 20 minutes to chill.
Grab your favorite heart-shaped cookie cutter (1.5 to 2.5 inches) and press it straight down, then lift straight up, to create your beautiful brownie hearts. You can wipe and lightly dust the cutter with a little cocoa powder as needed to prevent sticking.
Dust your delightful brownie hearts with powdered sugar, drizzle with a little melted chocolate, or add some colorful sprinkles for that extra festive touch. Enjoy your homemade, fudgy Valentine's treat!