This is kind of bad for you. But I don't care cos it makes me happy. Makes enough for two steaks plus extra to scrape up with your chips. Trust me, you'll be doing that.
large knob of butter
dash of olive oil
1 red onion, finely chopped
splash or two of brandy, can use sherry or white wine if you wish but brandy is best
1 oxo cube, crumbled into 100mls boiling water, stir to dissolve
2-3 tbsp green peppercorns, drained
Melt butter in a frying pan, adding oil to keep it from browning. Add onions and saute VERY gently on a medium heat so they get all sweet, soft and delicious. If you burn them start again.
Turn the heat up hot wait a minute then splash in your brandy, deglazing the pan.
Add stock and peppercorns and let it simmer for a minute.
Add cream then reduce, maybe 5 minutes on a medium heat. Your sauce should be thick and a nice creamy peanut butter colour.