I got all brave and cocky and made these for the first time over the weekend. It's not nearly as difficult or intimidating as I thought it would be.
You need parchment paper for this.

Make a pastry cream first:
Heat together on medium: 1¼ c. whole milk, ½ tsp. vanilla, a pinch of salt, and 2 T. sugar
In a separate bowl whisk together: 2 large egg yolks, 2 T. cornstarch, 2 T. sugar
When the milk is hot, turn off the heat. While whisking the yolks, add a little of the hot milk in batches to them to temper them. This will keep them from curdling. When about half the milk has been added to the yolks, add the tempered yolks/milk back to the sauce pan. Turn the heat back on, continue to whisk, and cook on medium about 2 more minutes. Turn off the heat and keep whisking. The mixture will become very thick, much thicker than pudding. That's okay - you need it to stand up to the pastry. If it starts to "bunch" up, add a little more milk and 1 T. butter and whisk some more. Cover it with a piece of parchment paper you've cut out to prevent it from skinning over, and refrigerate for at least two hours.

Make your pastry:
Thaw out a package of puff pastry (2 sheets) while you're making your pastry cream. (What, you thought I was going to tell you to make your own pastry dough? I'm a lot of things, but crazy is not one of them.) Pre-heat your oven to 400º.
Lay down a piece of parchment paper on a baking sheet. Sprinkle a work surface with sugar and roll out the dough to a piece that's large enough to fill most of the paper. Transfer to the bake sheet and lay another piece of parchment paper on top of that. Roll out the second sheet of puff pastry (using sugar on the work surface) to roughly the same size as the first and place on the parchment paper. Sprinkle liberally with sugar. Bake for about 20 minutes, or until the top has puffed up and is beginning to turn golden. When it's cool, place on whatever tray you want to serve (and cut) the Napoleons on, and separate the pastry layers. Place the top layer aside.

Make your icing:

Mix together: 1 c. confectioner's sugar, 1 T. melted butter, and 2 tsp. corn syrup. Add about 2 T. milk. Set aside a third of the icing and add 1 tsp. cocoa powder to it. Now you have both white and chocolate icings.

Assembly:

Spoon your pastry cream onto the bottom layer of pastry. Bring it out to the edges as best you can. Place the top layer of pastry back on the first, and using a spatula, press down. The sugar dome will shatter, but that's okay. Ice first with the white icing. Make stripes with the chocolate icing across the white, and then run your knife tip down the length of the pastry to create the feathered icing look.
Refrigerate another half hour or so. It'll make about 10 large Napoleons or a dozen smaller ones. Guaranteed to knock the ball out of the park.

Love to all!

Sounds wonderful!!!