The liquid looks wrong and is not. 375 ml will not cover the rolls, and it should not. Packed tight under a lid they braise in steam; a pot filled with stock gives you watery rolls and a thin sauce.
Line the pot and cover the top. Bacon and the small inner leaves underneath stop the bottom layer catching. A few spare leaves laid over the top stop the uppermost rolls drying out.
Do not work the filling. Fold it together until it is just combined. Overmixed mince goes springy and stays that way.
Cook the rice first. Raw rice keeps swelling in the pot and splits the leaves.
Yield: about 17 to 20 rolls from a large sweetheart cabbage. Any filling left over once you run out of leaves fries well as small patties.
They are better the next day. Cool them quickly, refrigerate, and reheat gently until piping hot through.
Salt the blanching water, and keep it plain. Salt speeds the softening; acid slows it right down, which is why the tomato sauce goes on at the end rather than the rolls being cooked in it from the start.