This is my ungulate ear pattern - a pattern is a good thing to have because 1) you can insure that both ears match perfectly and 2) 6 months down the road, when you want to make another set of ears, you will have forgotten what shape you used for the first pair.
It is cut out of thin cardboard and I drew an arrow on it to represent the fur direction - nothing is worse than cutting a pattern out and finding the pile is going the wrong direction - and I also labeled the top and the bottom of the ear.
Here I have used my ear pattern to cut out 3 pieces out of different fabrics - One is the outside of the ear (a short pile brown), the inside of the ear (an off-white felt), and the cartilage (stiff black felt).
The outside is about a 1/4 inch larger on all edges than the inside - this is easily done by tracing the pattern with a felt, and then cutting outside the line of the felt for the outside of the ear and inside the line for the inside ear.
The cartilage piece is the smallest of them all.
Here I have sewn the back and front together inside out, making sure to match the wrong sides of the fabrics. You can see how puckered they are - if your ears are perfectly flat, then you didn't match the edges of the inside and outside as you sewed.
Here they are turned right side out, and the black piece of felt has been placed inside the ear on the left. You can see how much flatter and smoother it is than the one without pseudo-cartilage.
I added some paint to the ears before finishing them, since it is much easier to do while they're still flat.
The paint smears on the right shows what colours I used - a flesh tone to over the inside of the ear to indicate visible skin (since the inside of a deer's ear is largely hairless) and a brown for shading deeper inside the ear.
I sewed the inside of the ear to the cartilage. This just makes things look a bit cleaner and neater when the ears are mounted.
I did not sew it to the back of the ear because then the thread would show - it is much more hidden inside the ear.
The finished product after bending over the two bottom corners at the base of the ear and sewing them together at the inside of the ear. This gives the ear a nice curve.
This is not the only way to finish them off, you can change things around depending on the look you want and how you plan to mount them to the head or headband, but this gives one of the cleanest results.
I may continue this, and show how I end up mounting them to the head. It's not something I can explain otherwise, as it differs based upon the particulars of the head and the expression I want.