Wash, pit and stem the four pounds of cherries. Cut cherries in half and divide in half. Two pounds goes into a large sauce pan. Reserve the other two pounds for later. Along with the cherries in the sauce pan combine sugar, lemon zest, lemon juice, sherry and place over medium high heat for 20-25 minutes, stir occasionally. The cherries will release their juices and create a large amount of liquid. After 20-25 minutes take the sauce pan off the heat and remove the cherries and lemon zest with a slotted spoon.
Place cherries in a strainer and press with the back of your spoon to release all the remaining juices. Pour juice into the sauce pan. Turn heat back onto medium and add nutmeg, honey and vanilla. In a small bowl combine water and cornstarch to create a slurry. Slowly whisk into the cherry sauce. Bring to a low boil to let the sauce thicken a bit. Take off heat once it reaches your desired consistency. Off the heat add the butter and stir until melted to create a beautiful silky sauce. Place sauce in a bowl and cover with plastic wrap right on the surface and chill in the fridge for one hour.
After an hour combine the remaining cherries with the cooled sauce. Serve over vanilla ice cream. Store in an air tight container for up to a week in the fridge.