A friend visited Croatia and raved about a dessert that sounds very similar to your vanilla slice. I love custard in anything. A local friend who recently passed had >70 hens and gave us lots of eggs. Those eggs and local Amish honey made a wonderful lightly-sweetened baked custard that even my husband liked.
Since we live in the middle of nowhere, I've never even seen puff pastry here. It sounds delicate like something I'd tear apart trying to work. (Some of us have the touch, and then there are the rest of us. A cake decorator who appeared on "The Chew" actually made gorgeous rosettes while he was blindfolded! That guy was fantastic.)
Sorry I blathered on so much, but I've saved some of those for years.
I love custard, too. I have an easy stirred custard you cook on top of the stove (carefully so it won't scorch but it works). It's not as solid as the baked kind but very tasty.
Puff pastry is available at most supermarkets in the frozen section. Pepperidge Farm is the most common variety. It's an awful pain to make it, never tried.
I found people raving over a slice that looked delicious on food.com, read the ingredients, 1 cup custard powder. And that stuff is expensive. I can certainly forgive people allergic to eggs to use it, and I only cooked some up once.
Lots of baked goods you have probably bought and eaten over the years consist of puff pastry, not anything that uses cream puff dough though (choux?)
There are some easier recipes on the web, but they aren't easy enough for me. If you do find and buy frozen puff pastry, it probably should be rolled a little bit.
You might get by with Pillsbury crescent roll dough that isn't perforated, comes in a sheet. In the refrigerated section in a can you have to hit on a seam to open. Then roll it fairly thin and prick it like a pie crust.
Maybe they don't have that in your parts. Too many choices. Walmart has Pepperidge Farm.
P.S. Greeks make a custard slice called Galaktoboureko, have no idea how to pronounce it. For the top and bottom, they use filo dough (which I tried once also used in that baklava recipe somebody posted). It's tricky, have to keep it moist and handle carefully. It does look delectable and maybe if a good Greek cook made it, I would like it.
For the custard I got some semolina flour through Amazon and made just the custards in muffin tins (don't need a hot water bath for that kind of custard). It gets very thick and has eggs and vanilla in it, but I didn't like that either.
Usually it's a little deeper yellow than in the photo.
The filo pastry would be just as hard to find or moreso than puffed. It's also in the frozen section of the larger stores. But I think I would like mine made with real pastry cream and filo, too, if it doesn't have too much butter slathered on the sheets, at least the powdered sugar top doesn't.
