Your partner opens 2NT (20-21) in 2nd seat, making you “captain of the hand”. Assuming that RHO passes, what is your plan to direct the remainder of the auction? Here is your hand:
Your worry about the diamond void makes this a difficult problem. It looks like you have enough to be in game, holding ace of hearts and a runnable club suit. It will be best if you discover an 8+ spade fit. So, you respond three hearts, transferring partner to three Spades. But what do you do after that?
Knowing that partner will bid game in spades with at least three of them, bid 3NT. Yes, diamonds are causing you discomfort. But should partner have only two spades, she is likely to have diamonds well stopped. Don’t chance leaving partner in a 7-card spade fit opposite 5 crummy spades.