You'll need to crush the peppercorns first, and this can present one or two problems.
If you've got a pestle and mortar you're home and dry; if you haven't, then the best way to crush them is by exerting a lot of pressure on the back of a tablespoon with the peppercorns underneath it. This last method can often result in one or two peppercorns escaping and rolling off on to the floor, if you're not careful. So be warned.
When you've got the peppercorns coarsely crushed, add them to the flour with the salt. Then dip the pieces of liver in it, pressing the pepper in a bit on both sides. Now in a large heavy-based frying pan, heat the oil and butter to the foamy stage, then put the liver slices in and cook them gently for a minute or two. As soon as the blood starts to run, turn them over, and gently cook them on the other side for slightly less time. Whatever you do, don't overcook the liver or it will be dry and tough.
Transfer the slices of liver on to a warm serving dish, add the wine to the pan, turn the heat up to let it bubble and reduce, then pour it over the liver and serve immediately.