Melt butter in a saucepan over medium heat.

Add finely chopped onion and sliced celery ribs to the saucepan.

Fry gently for 5 minutes, until the vegetables are soft but not browned.

Stir in flour and cook for 1 minute to create a roux. Remove from heat.

Stir in white wine and chicken stock until well combined. Return to heat.

Bring the mixture to a boil, stirring continuously, until the soup thickens.

Reduce heat to low and simmer for 30 minutes.

Cool the soup slightly.

Liquidize the soup using a blender, or press it through a sieve for a smoother texture.

Return the pureed soup to the rinsed-out pan.

Add milk and heat gently, without boiling.

Stir in crumbled Stilton cheese, grated English Cheddar cheese, salt, pepper, and heavy cream.

Continue stirring until the cheeses are melted and the soup is smooth.

Do not let the soup boil at this stage, or it will curdle.

Serve hot, garnished with croutons.