In a large mixing bowl, cream together the sugar and butter.
Mix in the flour and quick-cooking oats.
Add the boiling water and baking soda. Mix well.
Your dough will be very runny but do not worry, it will firm up for baking.
Freeze or refrigerate your dough depending on your preferences. See Options Below
Option A: Freeze & Slice
Lay out three sheets of wax paper and divide your dough in thirds between the three sheets forming a thick rope down the center. Roll and shape the dough in the wax paper. Freeze dough for at least 8 hours before slicing and baking. Following this option, your cookie will be more rectangular in shape due to the soft dough shaped in the wax paper and slicking the frozen cookie dough. You'll want to be mindful of forming a consistent dough amount throughout the length of your wax paper so you have cookies that match during the assembly process. If circular cookies are your preference, you may try using a slice and bake keeper to help retain the shape of your dough as it freezes.Just before baking, remove the frozen dough from the freezer, unroll, and slice a generous 1/8" thick. Place cookies on an ungreased cookie sheet.
Option B: Refrigerate & Scoop
For a consistent-sized cookie, this is the easiest and requires less time to cool the dough. Simply cover and refrigerate your mixed dough for at least 4 hours. Scoop the cookie dough onto an ungreased cookie sheet. With a glass dipped in flour, press cookie dough down lightly so it is uniform in width (about 1/8" thick).The best cookie scoop size for these cookies is 1 tablespoon size.
Prepare Date Filling
While your dough is chilling or freezing (depending on which option you chose) you'll want to prepare your filling.
In a saucepan combine chopped dates, water, and sugar. Bring to a boil.
The mixture is ready when it has thickened. This happens quickly, so keep a close eye on the mixture and continue to stir as it comes to a boil. Let the filling cool completely before assembling sandwich cookies together.
Let the filling cool completely before assembling sandwich cookies together.
Bake Cookies
Preheat oven to 325°F.
Bake for 10 to 12 minutes, or until edges are very lightly browned.
Once the cookie sheet is removed from the oven, quickly transfer the cookies to the cooling rack.
Allow the cookies to cool completely before spreading with the date filling.
Assemble Cookies
Spread about a scant tablespoon of the date filling onto the flat side of one cookie, then sandwich with another cookie, flat side down.
These cookies are so rich, you do not need to put a lot of filling in the sandwich.
Notes
Short Term Storage: Store assembled cookies in an airtight container for up to 5 days or for 7 days in the fridge. Using parchment paper between the layers is a good idea so the cookies do not stick together.
Long Term Storage: Freeze the cookies using parchment paper between layers in a freezer-safe container for 2 to 3 months.
Best Flavor: These taste the best straight from the freezer.