Trim the Brussel sprouts and blanch in a pan of boiling salted water for 6-8 minutes until just tender. Check by piercing with the tip of a sharp knife. Drain and cool quickly under cold running water, then cut each one in half. The blanched sprouts can now be put into a large Zip-lock bag and kept in the fridge until needed.
When almost ready to serve, heat the butter in a sauté pan and sauté the bacon until crisp and golden.
Add the pecan halves to the same pan and sauté for a couple of minutes until lightly toasted and sizzling.
Add the butter to the sauté pan and tip in the blanched Brussel sprouts, then sauté over a medium heat until warmed through. Season to taste and tip in the bacon and pecans and toss again briefly, then tip into a warmed serving bowl. Cover with foil and keep warm in a low oven until needed.