Oven too cold? Pastry too thin? Help!
Your oven was probably warm enough, although that's never a given unless you have an internal thermometer, but your pastry might not have been at the ideal temperature for baking.
It sounds like you rolled out the pastry yourself, which is where your problems might have started. You've got to be gentle but firm with it and and roll the pastry out evenly rather than bashing it into submission and messing with the layers.
When cutting you want to avoid using anything blunt and instead go for a sharp edge and cut in a clean motion, avoiding dragging the edge through the pastry as this will seal the layers together and spoil the rising.
The same goes for egg-washing. You only want to wash the surface areas and avoid getting anything dribbling down the sides as this, again, will spoil your rise. If you're baking twice, as it seems you were, I'd egg-wash on the second bake as this allows the pastry to rise and form a stable structure.
I'd suggest that 10-minutes is not long enough to properly bake the pastry through (you need all the moisture trapped between the layers to turn into steam - it's this process that puffs the pastry) and you ought to be looking at somewhere between 15 and 20-minutes to bake the pastry enough for it to hold firm and keep the filling where it ought to be.
Oh, and if you want to intentionally stop puff pastry from rising, poke some holes in it with a fork or other sharp object - this will let the steam escape. Just watch out for stodgy or uncooked pastry as the other areas will cook through faster.
And if you intend to pluck the middle out to fill it with something, lightly score a mark around the area with a sharp object but take care not to go through the bottom of the pastry itself. You can then cut through this 'lid' with a small knife and use a teaspoon to remove the inside.
