Tenderloin with Mashed Potatoes and Onion Sauce - Kookmutsjes

Ingredients

• 1100 g potatoes
• 4 g salt
• 0.5 g black pepper powder
• 0.5 g dried parsley
• 25 g butter
• 100 ml heavy cream
• 45 g butter
• 425 g beef tenderloin
• 3 g salt
• 2 g cayenne powder
• 2 g garlic powder
• black pepper powder
• 0.5 g fresh parsley
• 50 g butter
• 50 g yellow onion
• 20 g sweet soy sauce
• 300 ml heavy cream