You can make them into soup instead of just using them as part of a stock.
Mermaid soup
2 pints chicken stock
1 chopped onion
1 bunch beet tops, chard or spinach
couple of sheets egg noodles.
Cook the chopped onion and chopped greens in the stock until done. Add noodles and simmer for 5 minutes until noodles are done. Serve in bowls with toast cut into fishy shapes
greens and butter bean soup
1 leek
1 bunch greens
1 tin butter beans
2 pints stock, chicken or veg
1tspn chopped garlic
nutmeg, salt and pepper
Soften the leek in some oil or butter with the garlic. Add stock and chopped greens. Cook until tender. Add butter beans and cook another 10 minutes or so. Blend until smooth, season and heat through again. You can add a small carton of cream at this stage if you like.
Otherwise, use the beetroot tops as you would use spinach or chard, either as a vegetable (chopped and steamed with lemon and garlic is nice) or to make something like potato and greens curry or a cheese and greens quiche. You can also make them into a pasta sauce, either a tomato based one or a creamy one in a savoury white sauce.