Sorry to disagree with @DrMarkH but we found chard - stalks and green bits - to be surprisingly tasty.
My favourite for using the stalks @SuePJ is Hugh Fearnley-Whittingstall’s Chard Stalk Gratin. When my partner had to go on a vegetarian diet for a while, this was one of the dishes we actively enjoyed rather than tolerated 
Slice the stalks across in 1cm bits. A bit of oil and butter in a pan and fry them over a medium heat with some chopped garlic, stirring frequently, for 10-15 minutes until tender. Add chopped thyme leaves, salt and pepper and quite a bit of double cream. When bubbling, put into a gratin dish and scatter over grated parmesan/gruyere and breadcrumbs. Put under a hot grill until brown.
We eat it with new potatoes in season, or dressed puy lentils.