Combine milk and vinegar in a bowl. Let stand until milk curdles, about 5 minutes.
Preheat oven to 350 degrees F (175 degrees C). Grease a 12-cup muffin tin or line cups with paper liners.
Combine 1/2 cup butter, white sugar, and vanilla sugar in a large bowl; beat with an electric mixer until smooth and creamy. Add eggs one at a time, beating well after each addition.
Mix 3/4 cup plus 1 tablespoon flour, cocoa powder, baking powder, baking soda, and salt in a bowl. Alternate adding flour mixture and curdled milk to the creamed butter mixture, mixing until batter is well blended. Spoon batter into the prepared muffin cups, filling each 3/4 full.
Bake in the preheated oven until tops spring back when lightly pressed and a toothpick inserted in the center of 1 cupcake comes back clean, about 14 minutes. Cool in the muffin tin for a few minutes, then transfer to a wire rack to cool completely, about 1 hour.
Combine cream cheese and 1/4 cup butter in a bowl; beat with an electric mixer until well combined. Mix in vanilla extract. Stir in confectioners' sugar gradually. Color frosting green with a few drops of food coloring.
Place green frosting in a pastry bag fitted with a grass tip. Hold the pastry bag at a 90-degree angle 1/8 inch above the surface of a cupcake. Squeeze bag to form green 'fur' by pulling tip up and away when the icing strand is about 1/2 inch high. Repeat to cover cupcake evenly with fur. Add 2 eyes to each cupcake.