In a bowl, cream together ½ cup butter, a cup brown sugar and ¼ cup granulated sugar.
Add ¼ tsp baking soda, an egg, a tsp vanilla, and 1¼ cups all purpose flour. Mix thoroughly.
Add ½ a pack Mini Cadbury Chocolate Eggs and mix until the eggs are crushed.
Press dough into a lined and greased 9"x13" baking dish. Crumble ½ a pack Oreos over top, and press into the dough slightly. Drizzle ½ a can of sweetened condensed milk evenly over cookies. Crumble the other ½ of the Oreos over the top. Again, drizzle the remaining sweetened condensed milk over the cookies.
Bake at 180°C for 30-35 minutes, until edges are golden brown and pulling away at the sides.