Grease a 9"x13" pan and preheat the oven to 350 degrees Fahrenheit.
In the bowl of an electric mixer, cream together butter, brown sugar, granulated sugar, eggs, peanut butter and vanilla extract.
In a separate bowl, stir together oats, flour, baking soda and salt.
Add the flour mixture to the wet mixture and mix just until combined, scraping down the sides of the bowl in between.
Crush 1 c. of Cadbury Mini Eggs and stir them into the dough.
Press the dough into the prepared pan. Sprinkle with whole Cadbury Mini Eggs (the rest of the package and more if you'd like) and press them slightly into the top of the dough.
Bake for approximately 17-19 minutes, or just until the cookie bars are set and not jiggly or gooey. Be careful not to over bake. Allow them to cool completely on a cooling rack, then slice and serve.