This deal was played in the South Florida Bridge Players IMP game. South held:

 
K J 10
Q J 4
A K 7 5
A K 10
His partner, North opened 1. Most of my students would use Blackwood, but it is premature to do so. How can it hurt to start with an exploratory 2? Partner raises to 3 and now you show your heart support--3 (assuming you are in a 2/1 Game Force auction, of course).

All partner can do is bid 4. He has shown no sign of life; no slam interest. Of course, you were always going to insist on at least a small slam with your 21 HCP. Since partner has shown a minimum, it makes sense to give up on a grand slam. You can check on keycards if you wish (there are enough) and then settle into 6NT.

The Q is led and you see:

A 3 K 7 6 3 2 Q J 10 9 2 6
K J 10 Q J 4 A K 7 5 A K 10

Partner had a really nice hand in support of diamonds, but overall he is sure light on HCP. Given that the A is missing, I'd say 7 would not have been a good idea!

Meanwhile, how will you play 6NT?

At notrump, count winners.

You have 2 in each black suit and 5 diamonds for 9. If hearts behave you are in great shape.

Surely, your plan is to knock out the A, but how?

On 3-2 hearts you will soon claim, but what if they are 4-1? If the singleton is the ace, you are in business, as long as you start hearts from the correct hand. If RHO has a singleton ace, it will pop up if you lead a heart from dummy. If LHO has a singleton A, it will pop up if you start hearts with a low one from hand. If one opponent has a low singleton, you still have lots of chances, but why not cater to a singleton ace.  You can claim if either opponents has a singleton A. How?

First get rid of their diamonds. Cash some diamonds ending in dummy (they split 2-2). Now lead a low heart from dummy. If East hops with the ace, your troubles are over. If West wins you are also in great shape. If it was singleton, he will have to return a black suit, instantly giving you your 12th trick.  This was the Real Deal:

Vul: East-West Dlr: North	A 3 K 7 6 3 2 Q J 10 9 2 6
Q 9 6 2 A 8 3 Q J 9 5 3 2		8 7 5 4 10 9 8 5 6 4 8 7 4
	K J 10 Q J 4 A K 7 5 A K 10

After you win the club lead, cash some diamonds and play a heart to your queen, the hand is over. West takes his A, and his black-suit return instantly give you your 12th trick.

Of course, if hearts were 3-2, you would also have been in business. What if hearts were 4-1 without a singleton ace? Then you would have to play on and use your wonderful card-reading skills to produce 12 tricks.