Bring a medium pot of water to the boil. Blanch the stems of PSB in the boiling water for 2 minutes max. Transfer to a bowl of cold water to stop them cooking. Set aside.
In large deep frying pan over medium heat, add the butter and the olive oil. Bring to temperature until the butter is melted. Add the shallots and fry for a minute or two until turning translucent. Add the garlic and fennel. Season. Cook for a further two minutes, stirring regularly, until the fennel starts to turn translucent.
Add the white wine and cook until almost all the liquid has evaporated (a few minutes). Add the cream, water and the PSB stems and leaves. Cover with a lid and cook for a further 3-5 minutes until the PSB is cooked through.
Once the PSB is cooked but still nice and bright in colour, turn off the heat, add the lemon juice and stir through the oregano.
Check for seasoning and then serve with either fresh pasta or boiled new potatoes.