(sorry about the bad phone pic but that's all I had)
Boil 4-5 peeled yams for 20 minutes. Cool, then slice. Peel 4-5 apples and slice. In a buttered casserole dish alternate starting with apples and ending with yams (or just mix together). Meanwhile make sauce...
2 c. water
3-4 Tbs. corn starch
1 c. sugar
1 stick butter
1 tsp. salt
Cook sauce over medium heat until thick and clear. Pour over yams and apples and bake at 350 degrees for 1 to 1 1/2 hours.