Singleton Club – Responder – 1♢-2♢

Singleton Club – Responder – 1♦-2♦

N
W   E
 
S
♠ K 4
♥ 5 3 2
♦ K 10 4
♣ A K 9 6 4

Dealer:

West

W N E S
1♦ Pass 2♣ Pass
2♦ Pass ?

Partner opens 1♦ and we have a strong hand. They are unlikely to have five hearts when opening 1♦, so a direct 3NT is perfectly sensible. But we decide to bid 2♣ anyway, and partner rebids 2♦. What should we bid?