Line a baking sheet with parchment paper and set aside. Preheat your oven to 350°F so it's ready when you need it. Measure out all your dry ingredients (flour, baking soda, salt, cocoa powder, espresso powder, and pudding mix) into a small bowl and whisk them together to evenly distribute the leavening agents and cocoa. This ensures your cookies will have consistent flavor and texture throughout.

Using an electric mixer, beat the room-temperature butter with brown sugar and granulated sugar for 2-3 minutes until the mixture is light, fluffy, and pale. This creaming process incorporates air into the dough, which helps the cookies rise and creates a better texture. The Kerrygold butter adds a subtle richness that elevates these cookies.

Add the room-temperature egg, vanilla extract, and water (or coffee for deeper chocolate flavor) to the creamed butter mixture. Beat on medium speed for about 1 minute until everything is well combined and the mixture looks slightly curdled—this is normal. I prefer using a tablespoon of strong coffee instead of water here; it enhances the chocolate without making the cookies taste like coffee.

Add the dry ingredient mixture from Step 1 to the wet ingredients from Step 3, mixing on low speed just until the flour is fully incorporated. Don't overmix—stop as soon as you no longer see streaks of dry ingredients. Overmixing develops gluten, which can make the cookies tough rather than tender and fudgy.

By hand or with a spatula, gently fold in the M&Ms and festive sprinkles until evenly distributed throughout the dough. Transfer the dough to the refrigerator and chill for at least 1 hour (or up to overnight). Chilling prevents the cookies from spreading too much during baking and helps them maintain their shape and fudgy texture. I always chill my chocolate cookie doughs—it makes a noticeable difference in how they bake.

Remove the chilled dough from the refrigerator. Using a 2-tablespoon scoop or your hands, form the dough into balls and place them on the prepared baking sheet, spacing them about 2 inches apart. Gently press the top of each ball slightly to flatten it a bit, then top each cookie with a few extra M&Ms and a sprinkle of festive sprinkles for a Valentine's Day touch.

Place the baking sheet in the preheated 350°F oven and bake for 10-14 minutes, until the edges are set but the centers still look slightly underbaked and soft—they should jiggle just a bit when you gently shake the pan. Remove from the oven and let the cookies cool on the baking sheet for 5 minutes to set slightly, then transfer them to a wire cooling rack. This resting time on the sheet allows the cookies to firm up just enough to move without breaking, while finishing their gentle cooking on the cooling rack keeps them tender inside.