Melt the butter in a saucepan, add the broccoli and pine nuts and fry gently for three minutes. Add the lemon zest and juice, season well with salt and freshly ground black pepper and remove from the heat.
Cook the penne according to the packet instructions and drain, leaving a little of the cooking liquid in the pan. Add the broccoli mixture to the cooked penne, drizzle over the olive oil and stir well.
To serve, spoon into a serving bowl and scatter with grated pecorino.