What is this small plant with tiny white flowers and tiny saw-teethed leaves?

Question

I got a small plant (from my mother-in-law... ) on which I would like to have an ID with your help. I cannot say much about its life-cycle as I only got it recently: she told me it was once in a pot and she put it outside. Thus I assume it survived winters with peaks down to -20 C.

• tiny white flowers (1.5cm in diameter)
• saw-teethed leaves (2cm long, 1.5 large, reminds me of birch-leaves)
• flowers die back quite fast (a few days), but new one are coming out again quickly

Some images (click to enlarge)

Answer 1

Looks like some species of campanula like Campanula carpatica.

This spring I recieved one campanula carpatica as a gift in a pot. I planted it outside in June as it was overgrowing the pot and I heard it can withstand the colds of the winter.

I can't say it has been doing great outside, but it is still alive.

Answer 2

It is Campanula, but its not C. carpatica - it looks remarkably like C. trachelium 'album plenum', the so called 'nettle leaved' campanula, but that has flower stems which reach 80 cm, which is why I asked about the height...