Hi
I have a recipe from martha steward for homemade oreos. But it says that the cookies are only good for 2 days wit hthe filling on it. Do you think that it could be extended at all? and why do you think the time frame is so short?
Oh, I misread your post -- I thought you were asking for an oreo cookie filling recipe. So we can answer your question properly, can you clue us in to what her recipe for the filling is?
I'm not sure what the MS recipe is but I made homemade oreos using a chocolate sugar cookie then filling them with a stiff bc then I dipped them in melted chocolate. They should last a couple of weeks as long as they are in a sealed container. I had posted a picture of them but it was removed because they were not "decorated". HTH
Ingredients
* Vegetable oil cooking spray
* 3/4 cup all-purpose flour, plus more for dusting
* 1/3 cup unsweetened Dutch-process cocoa powder
* 1/8 teaspoon salt
* 6 tablespoons (3/4 stick) unsalted butter, softened
* 3/4 cup confectioners' sugar, sifted
* 1 large egg
* 1/2 teaspoon pure vanilla extract
* Sandwich Cookie Filling
Directions
1. Line baking sheets with parchment paper; lightly coat with cooking spray. Whisk together flour, cocoa, and salt. With an electric mixer on medium-high speed, cream butter and confectioners' sugar until pale and fluffy. Beat in egg and vanilla. With mixer on low speed, gradually add flour mixture, beating to combine. Divide dough in half; form into disks, and wrap in plastic. Chill until firm, at least 2 hours, or up to 2 days. (Dough can be frozen up to 2 months; thaw in the refrigerator before using.)
2. Working with one disk at a time, roll out dough to a 1/8-inch thickness on a lightly floured surface. Using a 1 1/2-inch square biscuit or cookie cutter, cut out shapes, transferring to prepared sheets (1 inch apart) as you work. Chill in freezer until firm, about 15 minutes. Brush off excess flour. Gather together scraps; roll, chill, and cut out more shapes.
3. Preheat oven to 325 degrees. Bake cookies, rotating sheets halfway through, until edges are firm, 12 to 14 minutes. Transfer cookies, on parchment, to a wire rack to cool completely.
4. Spread a small amount of filling on the bottom of half the cookies. Top with remaining cookies; gently press to adhere. Assembled cookies can be refrigerated up to 2 days in an airtight container.
hope this explains it more 
Okay if I'm reading that right she doesn't give the recipe for the "sandwich filling". In that case I don't know why she says the cookies will only last two days. I have a recipe for the filling itself and that can last for quite some time. Baked cookies can last up to 2 months stored airtight (not that they ever last that long around here...) 
Sorry, I'm not sure what Martha was thinking...
Could be the cookies become soggy if the filling is in them for more than 2 days?
OK, I looked up the recipe for the filling:
3/4 cup butter
2 cups powdered sugar
flavoring
Maybe the butter fat seeps into the crisp cookie and softens them!
That's it, it's the butter in it. The recipe I have uses shortening instead.
For my homemade Oreos I just use a buttercream frosting that I make a little thicker. Also, I have kept them for up to two weeks. They stay soft for the first two weeks or so and then get rock hard.
bobwonderbuns, would you mind sharing your recipe?
And also I was going to sub margerine for the butter, would that make a diff?
The recipe I have is years old and I believe it's an old Todd Wilbur recipe (Mr. Top secret recipes himself.)
3 1/2 Cups powdered sugar
1/2 tbsp granulated sugar
1/2 tsp Vanilla
1/2 cup shortening
3 TBSP hot water
Mix well.
As for your question about the margarine, I'm not really sure how much of a difference that would make. I don't like the taste of margarine and I never use it in my frostings but that's just me. In this recipe I gave you there's no need to refrigerate so your cookies should last a lot longer than two days. Try it an let us know how it works! 
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