Creamiest Cheesy Potatoes au Gratin – Culinary Heirloom

Ingredients

• 1 tbsp olive oil or vegetable oil
• 1 cups onions
• 2 shallots
• 2 garlic cloves
• 4 tbsp butter
• 3 tbsp flour
• 2 cups whole milk
• 1 cups heavy cream
• 1 1/2 tsp kosher salt
• 1/2 tsp ground white pepper
• 8 large russet potatoes
• 3 cups shredded Cheddar cheese
• 1/4 cups Parmesan cheese