Preheat oven to 350 degrees.
In the bowl of a stand mixer, cream together the butter, sugar, and brown sugar using the paddle attachment. Mix until light and fluffy, or about 3 minutes. Add the eggs and vanilla slowly, scraping down the bowl as needed.
In a separate large bowl, combine the flour, baking powder, baking soda and salt and whisk to mix.
Add the dry ingredients to the butter mixture, then mix on low speed just until combined. Finally, add the M&M's and Mini Cadbury Eggs, reserving about ¼ cup of each to add to the baked cookies, and mix on low speed to combine.
Use an ice cream scoop or spoon to scoop 2" balls of dough, placing them about 1-2" apart on a parchment lined baking sheet.
Bake for 10-12 minutes, or until golden brown on the edges.
Remove the cookies from the oven and add immediately a few of the reserved chocolate eggs and M&MS to the cookies, if desired.
Allow the cookies to cool on the baking sheet for 5 minutes before transferring to a cooling rack to cool completely. Enjoy!