Place raisins and water in a blender and puree until smooth. Set aside.
In a large bowl, beat together butter, brown sugar, and granulated sugar.
Add the eggs and continue beating until creamy.
Mix in the raisin puree and vanilla extract.
Mix in the flour, beating just until combined.
Stir in oats and raisins or nuts if using.
Cover and chill for 1 hour.
Place parchment paper on baking sheets, set aside. Preheat oven to 350 degrees.
Scoop cookie dough and place on baking sheets. I used a #30 cookie scoop, about 2 Tablespoons.
Bake cookies for 10 to 11 minutes, until edges are lightly browned and center is set. They will look under-cooked, that's okay.
Place cookies on a wire cooling rack and allow to cool completely!
To Assemble
Place a scoop of ice cream in the center of an Oatmeal Cookie {I used a #16 scoop} and then top with a second cookie.
Press down just enough to push the ice cream to the edges of the cookie. Place them in the freezer for about an hour to harden. I put them in the freezer uncovered, on a parchment paper lined baking sheet.
For the Chocolate Coating
Place bittersweet chocolate and oil in a bowl and microwave on HIGH for 1 minute.
Stir, and microwave for an additional minute. Stir chocolate together until completely melted, placing back in the microwave in 15 second increments just until it is melted and smooth. Do not over heat the chocolate, or you will have to start over.
Remove the ice cream sandwiches from the freezer. Use a wire scoop {or any scoop that you have} to hold the ice cream sandwich.
While pouring chocolate over the top with a large spoon. Smooth the top with the spoon to remove the excess chocolate.
Place on the parchment covered baking sheet and place back in the freezer until hardened, about an hour.