Sauté onion and garlic in butter. Make sure your pan is properly heated before adding ingredients — you should hear a nice sizzle. Don't overcrowd the pan or things will steam instead of getting that beautiful golden color.
Add potatoes and broth.
Simmer 15 minutes until tender. Keep an eye on the heat — you want a gentle simmer with small bubbles, not a rolling boil. This helps develop flavor without overcooking.
Mash lightly for texture.
Stir in milk and season. Always taste as you go — you can add more seasoning, but you can't take it away!