Another recent forum discussion convinced me of the utility of an approach to handling one-of-a-minor raised directly to 3NT. What I propose as a sound agreement follows.
Opener bids his shortness with slam aspirations. 4D is long diamonds without shortness. Cuebidding follows, but 4NT is to play.
This leaves some questioning what to do if you opened 1D with six diamonds and five of a major. As I would only do that with "extras," I'll now bid five of the major as a pick-the-slam bid.
This also caused some to wonder what to do with 4-4 or 5-4 in the minors and no shortness. With that, I'll bid 4NT, after which minor-suit scrambling is allowed.
Finally, what to do with a minor two-suiter? That is "simple" but subtle. Opener shows his short major. If this is fitting, Responder (or Opener later, as the auction develops) can introduce clubs at the 5-level or 6-level, pass-or-correct. Thus, for instance, if Opener has 1354 pattern he can bid 4S after 3NT. If Responder can accept the slam try, he can, for instance, cue 5C. Opener might raise this to 6C, which Responder can convert to 6D.
What if 1D-P-3NT may feature a 4-card major? For those who do this, 1D-P-3NT-P-4C-P-4M can be natural, or 1D-P-3NT-P-4H-P-4S. With hearts, there is a problem if the auction goes 1D-P-3NT-P-4S. So, perhaps you should not bid 3NT with hearts if shortness in spades from partner might make 6H look good -- bid 1H with that hand.
The same structure of pass-or-correct does not work well, because the new strain (diamonds) outranks clubs. Now, some technique is needed.
Four-of-a-minor is a shortness bid, but each also promises four diamonds. Typical pattern is, for example, 1345 (4S). Now, Responder can select the game.
With short diamonds, bid 4D. Now, the minor two-suiter is not an issue. Hwever, if you insist that 3NT could hide a four-card major, then Responder should be allowed to introduce that major after 4D.
Without neither short diamonds nor long (4-card) diamonds, but long clubs, bid 4C. Responder can ask for shortness (4D), in which case you bid the shortness, or the appropriate level of NT for the strength with no shortness. For those who want to check back on a possible 4-4 major fit (those who might have a four-card major and bid 3NT), then you just bid the major directly over 4C, or wait with spades and hope for a 4H call.
You can, as always, also use a quantitative 4NT, or the 5-level major jump.