The fascia boards,banana cut look, on my house are nailed to rafter ends that are cut square to rafter. This creates a compound angle at butting ends at the inside/outside corners. How do I cut these?. David

Perhaps I am misunderstanding your post. I don't know what a banana cut look is but assume it is some kind of profiled fascia board. You said your rafter ends were cut square to the rafter. To me that means your rafters ends are cut 90 degrees to the length.

If my understanding is correct, your cuts for both pieces would simply be 45 degree bevels cuts at a 90 degrees to the length. In other words not a compound miter cut.

If by some chance you mean your rafters are cut plumb, that is straight up and down relative to the earth, and you have a profiled fascia board, the cut cannot be made. The profiles of the two pieces will not be aligned.

When you have a flat profile fascia (flat piece of 1 x 6) you trim off the bottom corner of the gable end piece (the one cut at an angle) to match the width of the eve end piece.

To illustrate, cut a piece of your fascia at a 45 degree miter. That is 45 degrees relative to the length. Measure the width of each aspect of the profile. Each aspect of the profile will be wider than the corresponding aspect when cut at 90 degrees.

In other words you can't change two directions with one cut. You must make a bevel cut (45 degrees) to go around the corner and then make a miter cut to go up the gable end of the roof.

Of course, I could be totally misunderstanding you post.