Line a 13x9" baking pan with foil, with ends extending over sides. Finely crush 24 cookies (I placed them in a Ziploc bag and crushed them with my rolling pin). Melt 1/4 cup butter; mix with crumbs. Press onto bottom of prepared pan.
Beat softened cream cheese and sugar with mixer until blended. Add sour cream and vanilla; mix well. Add eggs, 1 at a time, beating after each just until blended. Chop remaining 12 Oreo cookies. Gently stir into batter; pour over crust.
Bake for about 45 minutes or until center is almost set. Let cool (I stuck mine into the fridge for about 2 hours).
After the cheesecake has cooled down, microwave chocolate in a microwaveable bowl until melted (follow directions on packaging); stir until smooth.
Use foil handles to lift cheesecake from pan and cut into bite-size pieces. Place on baking sheet covered in wax paper.
Drizzle melted chocolate over each piece of cheesecake using a spoon. Stick in the fridge until chocolate has hardened.