- With the rack in the middle position, preheat the oven to 350°F (180°C). Butter the sides of two 8-inch (20 cm) springform pans with removeable bottoms. Line the bottoms of the pans with parchment paper.
- In a bowl, combine the flour, baking powder, baking soda and salt.
- In another bowl, whisk the brown sugar, sugar, mayonnaise, vanilla and eggs with an electric mixer until smooth. With the machine running on low speed, or with a wooden spoon, add the dry ingredients, then the chocolate chips. Mix for 1 minute or until smooth and creamy. Divide the mixture between the prepared pans.
- Bake for 25 minutes or until the cookies are nicely golden but the centre is still slightly soft. Let cool completely, about 1 hour.
- Unmould the cookies and clean out one of the pans. In the clean pan, place one of the cookies upside-down. Using a ¼-cup (60 ml) ice cream scoop, drop in the ice cream, alternating the flavours. Press down gently with a spatula into an even layer. Top with the second cookie, pressing down. Cover the pan with plastic wrap. Freeze for 8 hours or overnight.
- When ready to serve, let the ice cream sandwich sit out at room temperature for 15 minutes before unmoulding. Pass a warm blade between the sandwich and the side of the pan to help unmould. Cut into wedges and serve immediately.
The addition of mayonnaise in the cookie batter will prevent the cookies from getting too hard once frozen. You will still need to let the ice cream sandwich sit out for 15 minutes to soften slightly before serving.