Lay one sheet of phyllo pastry on your board with the long side facing you. Brush with oil or butter.
Scatter a few spoonfuls of the spinach artichoke filling over the phyllo. For my 13 x 18" phyllo sheet, I did 5 rows of 3 tsp of filling (as shown in video below). Each row was about 3" apart. Top with another sheet of phyllo and lightly press down with your hands. Brush the top of the phyllo with butter or oil. TIP: Less is more here. If you fill the phyllo sheets with too much filling, it will be difficult to fold.
Fold the filled phyllo sheets into a concertina (as shown in video below) starting with the edge closest to you. Each fold should be about 2". Then gently coil the phyllo into a spiral shape and place in the middle of the cast iron pan. TIP: Cover the cast iron pan with a damp towel while you fill the rest of the phyllo sheets.
Repeat with the remaining phyllo and spinach artichoke filling. Wrap each filled piece around the centre coil to form a large spiral (as shown in video). I ended up with 7 spinach artichoke filled concertinas.
With the remaining phyllo, brush one sheet with butter or oil and lay another sheet on top. Then brush the top with butter and fold into a concertina. Use these pieces to fill the outer edges of the pie until the layers reach the edges of the cast iron pan.
Brush with butter or oil and sprinkle the tops with sesame seeds. Bake in the middle of the oven for about 70-75 minutes until the tops become a deep golden brown.
Once out of the oven, let the pie cool down for about 10-15 minutes before serving.