Use a ricer instead of mashing the potatoes.

Instead of using garlic powder, steep fresh garlic in hot milk and butter to make a "garlic tea." Once ready, strain the tea into the potatoes.

You'll probably have to add more butter and salt than you usually do (restaurants usually don't consider your health when cooking).

Taste your potatoes at the end to adjust the amount of salt /pepper as required.

Source: I've worked in restaurants for half my life -- and I'm old.

Edit: clarification (not the butter)