Place the beetroot in a saucepan
of cold water, bring to the boil and simmer for about 25-30 minutes,
or until tender when pierced with the tip of a knife.
Drain, when cool enough to handle,
peel and chop.
Heat 1 tbsp of the oil in
saucepan, add the onion and cook, stirring, over medium heat for
5-10 minutes, or until golden brown.
Add the mustard seeds and cook,
stirring for 5 minutes.
Add the port, jam, vinegar and
beetroot, then simmer over medium heat for about 20 minutes, or
until syrupy.
Mash with a potato masher to break
up some of the beetroot, remove from the heat, season and leave to
cool.
Preheat the oven to 425F Gas 7.
Heat the remaining oil in a hot
frying pan and cook the beef for 2 minutes each side, or until well
browned. Cool slightly.
Coat the beef with an even layer
of mustard.
Place the fillet in a roasting tin
and surround with the whole garlic cloves.
Roast the beef for 20 minutes for
medium-rare, or until cooked to your liking.
Set aside to rest.
Mix together the sour cream and
horseradish in a small bowl.
Serve the beef either warm or at
room temperature with the roasted garlic, beetroot relish and a
dollop of the horseradish cream.