Beat butter, brown sugar and granulated sugar together until fluffy. About 3 minutes. Beat in eggs one at a time. Scraping down the sides of the bowl after each egg. Beat in vanilla extract.
In another bowl combine flour, malted milk powder, baking soda and salt. Slowly beat flour mixture into egg mixture. Mix well.
Fold in chopped malted robin egg candies and dark chocolate chunks.
Press cookie batter into a a 10 inch cast iron skillet. Bake in preheated oven for 25 - 35 minutes or until a toothpick inserted comes out clean.