Preheat oven to 400F. Line 12 muffin cups with papers or grease well.
Prepare topping by combining flour, cocoa powder, and sugar. Cut in butter and then stir in Oreo cookies. Set aside.
In a large bowl combine flour, sugar and baking powder. Cut in butter until it resembles gravel. Beat in egg and milk. Stir in remaining ingredients until moistened. Do not overmix. Fold in cookies. Fill muffin tins ⅔ full.and sprinkle with topping.
Bake 16 minutes or until a toothpick inserted removes clean. Cool 5 minutes and remove muffins to a cooling rack.
In a saucepan or better yet, in a water bath, melt white chocolate with shortening over low heat, stirring regularly. Quickly remove from heat and drizzle over cooled muffins. If the chocolate isn't drizzling beautifully, spoon it into a small sandwich bag and snip off a corner. Pipe over muffins.
Store any leftover muffins in an airtight container.
Notes
Recipe adapted from Taste of Home Oct./Nov. 1999
Recipe by Jellibean Journals at https://jellibeanjournals.com/chocolate-cookie-muffins/