The name for a round flaky pastry that has a chocolate cream filling in the middle

The difference is that in sfogliatelle the filling is made of Ricotta cheese, while in the Lobster Tail the filling is made of French cream.

Lobster Tail is not something prepared in Italy; you find it on New York City. I had to ask to friend of mine living in USA, to know what Lobster Tail pastry is.

A few things that I think will solve your problem.

1. Use powdered sugar instead of granulated. I find that makes for a much smoother end product and a silkier mouth feel.
2. Cream the butter and sugar together first and then add the nuts and other ingredients. This will add some fluffiness as the creamed butter/sugar mixture will allow it hold a little more air.
3. Add another egg (or just an extra yolk). This will create a thicker end product and allow it to set harder at the end.
4. add almonds to a custard filling recipe. You can side step your entire problem by picking out a pudding or custard recipe that fits what you want and adding course chopped almonds to it, or on top of it. It ain't authentic but it works every time.

Also: A link I found that most closely resembles the way I make it, that might help you out.