Creamy fisherman’s potato bake

Ingredients

• 800g medium potatoes
• 1 tbs olive oil
• 1 brown onion, diced
• 450ml cream
• 1 tbs Dijon mustard
• 100g grated cheese
• 1 tbs lemon juice
• 1 tbs parsley, chopped
• 200g frozen green prawns
• 1 cup frozen peas
• 210g tin pink salmon
• 20g butter