Mussels with creamed kale on toast

1kg mussels

100ml dry white wine

2 tbsp rapeseed oil

1 shallot, diced

3 cloves of garlic, minced

100ml cream

250g cavolo nero (kale), washed and chopped

2 sprigs parsley, chopped

1 lemon, juiced

Sea salt and cracked black pepper

To serve:

4 thick-cut slices of sourdough bread

2 tbsp butter

Wholegrain mustard