Spray a 9x13 pan, if you prefer a more traditional spanikopita (pie like) , use a round 2 quart casserole dish.
Begin by placing a sheet of phyllo, then spread melted butter, another sheet of phyllo more butter, and so on until you've used 1/2 the pkg. of phyllo....as you can see this is a lengthy process. It really works best if you have some one help you with this step.
Then spread the spinach mixture over the top of the pyllo.
Now continue with the rest of the phyllo, do exactly as you did in step 2 with the layering of the phyllo then melted butter. You will want to sort of pull the edges down around the spinach mixture.
When you have finished, cut some slits in the top of your phyllo. If you have any butter left over, drizzle it over the top.
Bake in a 350 degree oven for an hour to an hour and half.