At what levels do heroes in Hearthstone earn gold cards?

As you level up a hero in Hearthstone you earn gold versions of that hero's basic cards. For example the Druid earns a gold copy of Healing Touch at levels 15 and 20.

What gold cards do heroes earn at which levels?

The community over at Hearthpwn has compiled a list of Leveling System Rewards (which is too long to enumerate here). Additionally the article on leveling in Hearthstone at Gamepedia provides insight.

Here are some interesting points to take away from the articles:

• Gold Cards are earned one at a time. Unlike the basic cards, which are earned in pairs.
• Heroes also earn golden versions of the basic set of Neutral cards.
• Class specific gold cards are earned between levels 11 - 49.
• Above level 50 golden basic neutral minion cards are awarded.
• To earn all gold neutral cards a player will have to level every hero to 60.
• Gold cards are earned at levels: 15, 20, 23, 26, 28, 30, 32, 34, 36, 40, 42, 44, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59 and 60.