Preheat the oven to 350°F. Lightly grease a 9" x 13" pan. To remove the whole sheet of brownies from the pan at once, grease the pan, line it with parchment, and then grease the paper.

Add the eggs, cocoa powder, salt, baking powder, espresso powder (if using), and vanilla extract to a bowl. Beat at medium speed for 1 minute or until smooth.

In a medium-sized saucepan over medium-low heat, or a microwave-safe bowl, melt the butter and sugar together until the butter is completely melted. Then, continue to heat until the mixture is hot (about 110°F to 120°F) but not bubbling and becomes shiny. Add the hot butter and sugar mixture to the egg and cocoa mixture. Stir until smooth.

Add the flour and chocolate chips. Stir until well combined.

Transfer the batter to the prepared pan.

Bake the brownies for 28 to 32 minutes. The brownies are done when the edges are set, and the center looks moist but not undercooked. To ensure that the center isn't undercooked, insert a tester in the center and flick the surface of the brownies up a bit to ensure that there are moist crumbs instead of raw batter underneath the surface.

Remove the brownies from the oven and transfer them to a cooling rack. The brownies must cool completely before wrapping them in mochi.

Wrap any leftovers and store them at room temperature for 5-6 days, or freeze them for longer storage.

Whisk the glutinous rice flour and sugar in a heat-safe bowl, then add the water. Mix until smooth.

Stir in a small drop of pink food coloring.

Dip a pastry brush in water and brush down the sides of the bowl so there are no dry bits of flour.

Loosely cover the bowl with plastic wrap and microwave in a 600-watt microwave for 2 minutes. If your microwave's wattage is higher, adjust the time accordingly.

Remove from the microwave and stir. If it is still slightly opaque, microwave for another minute or until it achieves a bouncy consistency.

Stir with a wooden spatula dipped in water to build up the mochi's elasticity.

Transfer the mochi to a baking tray dusted with potato or cornstarch and form it into a log.

Cut into 5 equal-sized pieces.

Shape each piece into a little ball.

Cut 5 (1-inch) squares from the brownies. Save the rest to enjoy later.