In a large bowl, cream together the butter and sugar. Beat until light and fluffy. Add zest, lemon juice, egg, and vanilla. Scrape the sides of the bowl to mix evenly. Slowly incorporate the baking soda, salt, and flour. Cover and refrigerate until thoroughly chilled, roughly 2-4 hours or overnight.
Preheat oven to 350℉. Line a cookie sheet with parchment paper.
Scoop batter into 12 large balls. Smooth them and press down the tops slightly. Bake 12-14 minutes. Place the baked cookies on a cookie cooling rack.
Once cookies have cooled completely, spread vanilla ice cream on 6 cookies and make a sandwich by adding the remaining 6 cookies to the top.
Pour the rainbow sprinkles in a wide bowl. Roll the exposed ice cream in the sprinkles. Place the ice cream sandwiches back in the freezer to harden. Enjoy!
Notes
I used a fresh pint of vanilla ice cream but you could use any flavor! Strawberry would be good with lemon.