Line your baking sheets with parchment paper and preheat your oven to 180 °C // 356 °F top/bottom heat.
Start mixing the butter, brown sugar, and vanilla sugar with a kitchen machine (or hand mixer) at medium speed in a medium bowl until it's nice and creamy.
½ cup Butter, ¼ cup Brown Sugar, ¼ cup Sugar, 2 tsp Vanilla Sugar
Beat in the egg and sift the flour over the mixture. Be sure to fold it in.
1 Egg, 2 cups Cake Flour
Add half of the M and Ms to the dough. Be sure to stir well.
4.59 oz M and Ms
Next, scoop out the dough into balls using a small ice cream scoop.
Place the cookie dough balls on your prepared baking sheet with enough distance from one another that it won't crowd the tray.
Spread the remaining M and Ms over the cookie balls. You'll need to press down a bit, so they don't fall off while they're baking in the oven.
Bake on the middle shelf for 10-12 minutes.
After baking, let the finished baked cookies cool on a cooling rack for about 8-10 minutes and store them in an airtight container or cookie tin.