Chop the top and bottom off the bell peppers and quater the pepper lengthwise, trimming any seeds or white membrane from the inside. Lay the strips of bell pepper on a baking sheet skin side up. Move your oven rack to the top position and turn the broiler on high. Put the sheet of bell peppers directly under the heating element and broil until the skins are charred almost solid black. This gives the peppers a nice smokey flavour. Once charred, put them in a ziplock bag, and seal the top and allow to cool. The steam escaping from the hot pepper dislodges the charred skin so it is easy to peel.
Crumble the saffron into a bowl and cover with the water.
Peel the roasted peppers and cut them into thin triangular strips. Butter the bottom of a 9" round cake pan and lay the strips down in a circular pattern. It's okay if there are small gaps between the peppers. Make the caramel by adding the butter, sugar and cinnamon in a pot over medium high heat. Cook until the sugar is melted (there shouldn't be any granules of sugar left), but be careful not to burn it. Pour the mixture over the prepared bell peppers. The hot mixture may spatter, so please be careful.
Turn the oven on to 350 degrees F and move the oven rack to the middle position.
Whisk the masa harina, polenta salt and baking powder together in a bowl. Put the butter, light brown sugar and sugar to the bowl of an electric mixer and beat until smooth and creamy. Add the eggs one at a time and beat until incorporated. Add the vanilla, saffron and soaking water and continue beating then slowly add the milk until fully incorporated. Add the flour mixture in all at once, then beat until smooth.
Pour the batter in to the pan with the peppers and caramel and flatten off the top. Bake for 35-40 minutes or until a toothpick inserted into the center comes out clean. Remove the pan from the oven and let it cool enough to touch. Put a plate on top of the pan and flip it over to invert the cake onto the plate. If any of the peppers stay stuck to the pan, just remove them and put them back into place on the cake. Allow the cake to cool to room temperature then slice and serve.