Beat the butter, dark brown sugar, and granulated sugar on medium until light and fluffy.
Add eggs and vanilla and beat well.
Add flour, baking soda, and salt. Mix well.
Add the oats and raisins. Mix well.
Drop by rounded teaspoons onto ungreased cookie sheets. (I found that generous teaspoons were a better size for these cookies as larger ones were just too much "sandwhich" for one guest). Or use a small ice cream scoop for universal shapes.
Bake 8 to 10 minutes or until light golden brown. Cool for a minute on the cookie sheet, then remove to a wire rack to cool completely. Store in an airtight container or ziploc bag while you prepare the ice cream.
Vanilla Ice Cream
Heat the milk, half-and-half, salt, and sugar in a saucepan. Scrape the seeds from the vanilla bean into the milk and add the pod to the milk mixture. Turn off the heat and infuse the vanilla into the milk mixture for at least an hour.
Set up an ice bath (a smaller bowl placed within a larger bowl - the larger bowl filled with ice and a bit of water). Place a strainer in the smaller bowl. (The strainer will help remove any bits of egg that remain and produce a smoother custard).
in a separate bowl, whisk the egg yolks and add the warm milk mixture, 1/4 cup at a time, in a steady stream while whisking, to warm the egg yolks. Continuously whisking while adding the liquid here is important as it prevents the eggs from becoming scrambled. Scrape the warm yolks back into the milk mixture saucepan.
Cook over low heat until the mixture (custard) is thick enough to coat the back of a spoon. Strain the custard through the sieve and let it cool. Remove vanilla bean and save for other uses.
Freeze the custard according to your ice cream maker's instructions (depending on the brand you own).
To assemble: Remove ice cream from freezer and let soften slightly. Using a small ice cream scoop, sandwhich a scoop of ice cream between two oatmeal cookies. I wrap the cookies individually in parchment or wax paper and freeze them again for easy transport, or you can bring the cookies and ice cream separately and let guests make their own!