- Fold the 16 sheets of aluminum foil into 3 ½-inch (9 cm) wide strips. Roll 8 strips into cylinders the same diameter as the muffin cups.
- Place the strips upright in the muffin moulds.
- Loosely wrap the other 8 aluminum strips around the corks.
- With a rack in the middle position, preheat the oven to 350°F (180°C).
- In a bowl, combine the flour, baking soda and salt. Set aside.
- In another bowl, cream the butter and sugar with an electric mixer. Add the egg and beat until smooth. At low speed or with a wooden spoon, stir in the dry ingredients and chocolate chips.
- With a shot glass, press 1 to 1 ½ tbsp (15 to 22.5 ml) of cookie dough at the bottom of each muffin cup.
- On a work surface covered with parchment paper, roll out cup (75 ml) of dough into a 6 x 3 ½-inch (15 x 9 cm) rectangle.
- Remove the rectangle of dough from the paper or mat, flipping it onto one hand. Line the inner walls of an aluminum cylinder with the dough. With your fingers, press the dough at the lower end of the cylinder and the dough on the bottom of the mould together to seal the cookie. Repeat with the remaining dough.
- Place the wrapped corks in the cookies.
- Bake for 20 minutes. With tongs, remove the corks and bake for another 10 minutes, or until the dough is golden brown. Let cool completely before removing outer foil.
- With a brush, generously coat the inside walls of the cookies with melted chocolate to make them leak-proof. Allow to set completely.
- When ready to serve, fill the cookies with milk. Enjoy immediately.