I would vote for the Potter wasp. The nests of it look like a jug made out of mud.
The potter wasps have at least two generations each season. That might explain why you've had this nest twice. Of course I can't say that for certain.
But what really brought me to conclusion was your "some sort of larvae inside". The female potter wasp lays one egg in the nest. So, you actually have on larvae and it looks quite strange :):
After the female wasp shapes the mud nest, she places some paralyzed
caterpillars and an egg inside the jug and then seals the opening.
When the egg hatches, the wasp larva consumes the caterpillars. Then
it spins a cocoon within the mud cell. In the photo (above), I
have split open the jug to reveal the wasp larva. The larva is
protruding slightly from its cocoon.
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