Preheat your oven to 350°F (175°C). Line a large baking sheet with parchment paper.
In a large bowl, beat the softened butter with a hand mixer or stand mixer on medium-low speed until smooth and creamy.
Add the granulated sugar to the butter and beat until the mixture is fully combined and no visible sugar remains.
Add the egg and vanilla extract, then mix with low speed just until everything is incorporated. (Avoid overmixing, as beating the egg too long can make the cookies turn out stiff.)
In a separate bowl, whisk together the flour, matcha powder, baking soda, and salt. Sift the dry ingredients into the wet mixture, then mix on the lowest speed of your hand mixer until just combined. (Overmixing activates the gluten in the flour, which makes the cookies become dense and chewy in a bad way.)
Crushed mini eggs chocolates, gently fold them into the dough, saving a few whole ones to press on top later.
Scoop the dough into ¼-cup-size balls and place them on the baking sheet at least 2 inches apart.
Bake at 350°F (175°C) for 15 minutes. If you prefer softer cookies, you can reduce the baking time to around 12 minutes. I personally like mine with a crispy outside and soft inside, so I usually go for the full 15 minutes.
Remove the baking sheet from the oven. While the cookies are still warm, quickly press a few mini eggs onto the tops of each cookie for decoration.
Let the cookies to cool on the baking sheet for 10 minutes, then gently transfer them to a wire rack to cool completely.