When I make spinach dip, I use my food processor. I defrost the chopped spinach, rinse and press or squeeze out the water well. Then put that into the food processor and pulse until it is chopped finer. I then add the soup mix, pulse again and then add sour cream and/or mayo. Pulse again until it is fully mixed.
The end result is a much smoother blended dip, without chunks of unruly spinach or gritty areas of the soup mix.