Just made a recipe where I added a pound of apples to an APA.
Pealed, cored,and quartered the apples. Froze them to help break down cellular tissue. On brew day, I let the apples sit out and thaw (thew really turn to mush) and I threw them in a processor with about a half cup of water. Poured the mix in a small pot, and brought to a near simmer for about a half hour to sterilize the fruit. (I also added some clove honey to my recipe to add ABV and for some of the clove flavor, I put this in my apple mix). Then I added this mix the last 10 minutes of my wort boil.
I didn't want to add to my secondary and deal with cleaning a fruity-scummy carboy. Came out pretty good with a hint of apple. I've read that typical fruit beers use 5 pounds of fruit (never made one myself).