Heat oil in a large saucepan over medium heat.

Add chopped onion and sauté for about 8 minutes, stirring occasionally, until softened.

Add diced squash and vegetable stock to the saucepan.

Bring the mixture to a boil, then reduce heat and simmer for 20-25 minutes, or until the squash is tender.

Carefully transfer the soup to a food processor or blender and blend until smooth.

Return the blended soup to the saucepan.

Add milk and cream to the soup and gently reheat, being careful not to boil.

Stir in beer mustard to taste, then season with salt and pepper to taste.

Serve the soup hot, garnished with chopped parsley.