Substitute 1½ pounds cherries, pitted, for the peaches. Omit the sugar. Use ¼ cup kirsch in place of the Cognac. Do not poach the cherries, but add the white wine to the roasting pan in step 4. In step 5, add the cherries and kirsch to the finished sauce and simmer for 3 minutes. To serve, spoon the cherries and the sauce over the duck.