Pre-heat oven to 180°C: 350°F: Gas 4.
Wash the spinach and place into a saucepan.
Cover and cook for a few minutes, until wilted.
Drain well in a sieve, pressing with a wooden spoon to remove excess liquid.
Add 15g (½oz) butter, season to taste.
Arrange the spinach in four portions in a shallow ovenproof dish.
Top with slices of tomato, add the haddock fillets.
Cover with buttered baking foil.
Bake for 15-20 minutes or until the haddock flakes easily.
Place the remaining butter, flour and milk, in a saucepan.
Bring to the boil, whisking constantly, until the mixture boils and thickens.
Cook for a minute or two.
Remove from the heat.
Stir in half the cheese and reserve.
Poach the eggs.
Pre-heat the grill.
Place a poached egg on top of each haddock fillet.
Pour over the sauce, top with the remaining cheese.
Place under the grill for 2-3 minutes or until golden brown.