Melt butter in a non-stick pan, add refined flour and saute till lightly coloured. Add milk and stir continuously to avoid lumps.
When the sauce thickens add corn kernels and spinach and mix well. Add salt and crushed black peppercorns and mix well.
Put the mixture into a bowl. Grate cheese into the bowl and mix well.
Spread the mixture evenly on 4 bread slices, cover with the remaining slices.
Drizzle a little olive oil over each sandwich. Toast them in a hot grill till evenly golden on both sides.
Cut each sandwich into 2 pieces and serve hot.