Put the frozen spinach in a dish and defrost, uncovered, for 6 minutes in the microwave oven on HIGH.
Pour the spinach into a colander.
Remove the tough stalks from the watercress, rinse carefully and spread out on a plate.
Cover.
Microwave the watercress for 4 minutes on HIGH.
Drain in a colander.
Rinse the tarragon and parsley, pat dry on kitchen paper and remove the leaves from the stalks.
Discard the stalks.
Slice the pork and bacon into pieces.
Put the pork and bacon into a food processor and grind (mince).
Add the tarragon, parsley and scallions (spring onions).
Squeeze the spinach and watercress to extract as much liquid as possible.
Add to the food processor.
Add the garlic and puree again, gradually adding the eggs, nutmeg, cayenne pepper and salt and pepper to taste: this terrine should be highly seasoned.
Pour the mixture into a 2 quart (2 litre/3 1/2 pint) terrine dish.
Press down well with the palm of your hand.
Put the bacon strip (rasher) on top.
Cover the terrine and microwave for 25 minutes on MEDIUM-HIGH.
When the terrine is cooked, remove the cover, set a small plate with a heavy weight on top and leave to cool at room temperature.
Chill in the refrigerator for 24 hours.