I pretty much daydream about two things: houses and baked goods.
If you're not familiar with the cookies, they're like the inverse of Oreos - butter cookies on the outside, chocolate filling on the inside. My homemade chocolate buttercream tastes a lot like that filling.
So all I needed, really, was to whip up a batch of that, bake some butter cookies and sandwich them up.
I had a free afternoon yesterday, plus the weather is perfect for baking, so I decided to give it a try. The results are delicious - a little softer than the storebought kind, but the flavors are right on.
(And yes, I know a grim report about obesity was released yesterday  and I remembered that when I wanted to end this morning's dog walk early.)
Here's how I made them (and here's the source of my butter cookie recipe )
1 cup butter
1 cup white sugar
2 2/3 cups all-purpose flour
1/4 teaspoon salt
2 teaspoons vanilla extract
Cream together butter and sugar until fluffy. Beat in egg and then vanilla, then add flour and salt.
I rolled the dough in floured plastic wrap and shaped it into a square. I chilled it for an hour in the fridge. You could probably leave it longer than that, maybe even overnight as long as the plastic wrap is sealed well.
When you're ready to bake it, preheat your oven to 400 degrees.
I sliced the dough roll into individual cookies and should have been more careful about making sure they're even widths. (Mine didn't bake evenly.) I put them on silicone baking mats on cookie sheets, although the original recipe calls to bake them on ungreased chilled cookie sheets.
Don't crowd your cookie sheets, a lesson I also learned the hard way. Because you're making sandwich cookies, you want them to retain their square shapes. This doesn't work if they slide down the silicone mat into a shape that reminded me of learning about the Pangea supercontinent in fourth grade. 
Cool your cookies completely on wire racks.
Chocolate Buttercream Frosting
1/4 cup solid vegetable shortening
1/4 cup butter, softened
1/3 cup cocoa
1/2 teaspoon vanilla extract
2 cups confectioners sugar, sifted (add more for thicker frosting)
2 tablespoons milk (add more for thinner frosting)
In a large bowl, mix together shortening and butter with electric mixer. Gradually add in cocoa. Add vanilla.
Carefully mix in sugar, one cup at a time. Scrape sides of the bowl every so often. Add milk until the frosting is fluffy. If you want your frosting to be stiffer (which might be better for sandwich cookies), add a little more sugar until it's the texture you desire.
I made this frosting while my cookie dough was chilling, and kept it in the refrigerator until the cookies were totally cool.
Add a generous amount of frosting to one cooled cookie, and top with another to make a sandwich. I let them sit and harden on my counter for probably almost an hour. This allows the frosting to get a little crusty and keeps them from getting too mangled when you store them. I put mine in a sealed Pyrex container and left it on the counter, rather than the fridge. I didn't want condensation making them any softer than necessary.