Preheat the oven to 350 degrees. Line 2 rimmed half sheet pans (13 inches x 18 inches) with aluminum foil or parchment paper.

In a standing mixer with a whisk attachment, or using a large bowl and a hand mixer, mix the eggs and sugar until they are pale yellow and fluffy, about 8 minutes.

Add the melted butter, sour cream, the baking soda dissolved in vinegar and mix to combine.

In another medium bowl, mix the flour and cocoa together or sift into the batter. (The cocoa tends to get lumpy, so it helps to give it a good stir.) Add to the batter and mix to combine.

Divide the batter evenly between the 2 prepared baking sheets. Bake in the preheated oven for 18-20 minutes. Cool.

Meanwhile, make the filling. Mix all the ingredients in a standing mixer with a paddle attachment or using a hand mixer until evenly combined.

You can be as creative as you want at this point, by creating different shapes, etc. I decided to make small squares this time. Cut the pastry sheets into 1 ½ inch squares. (It really doesn't matter on the size; I'm just telling you the size that I made this time.) Set aside all the trimmings and pulse them in a food processor to make crumbs. You can also combine the crumbs with finely chopped nuts.

Spread the filling on top of a piece of square and sandwich another square on top of it. Spread the filling all the way around the square and coat it completely in the crumbs. Repeat with the rest of your little squares. I actually like to cut the squares in half horizontally and put filling in between them, and then place 3-4 thin squares together so that they have more filling, more flavor and are even more tender.

I got about 70-80 little squares out of this batch of 1 ½ inch pieces. Keep in mind that you will need to use part of the pastry for crumbs. You will also have some of the filling left over, however, if you cut the little squares in half, you may use up all of it.