Heat a small heavy pan over medium-high heat. Add butter, onions, and sugar and cook, stirring often, until onions have softened and picked up color, eight to 20 minutes. Stir often, especially at the end of the cooking time.
Roasted Red Bell Pepper:
Place a generous amount of foil on a sheet tray, enough foil to fold over the bell peppers and crimp tightly. Add the bell pepper quarters in a line, turn the foil up a bit on the edges to contain any juices. Broil about four inches below the broiler until the skin is charred and blistered. Remove from oven, fold foil over the peppers and leave to steam for several minutes. Open packet carefully, peel peppers and slice peppers into strips.
For the Panini:
Preheat grill or panini pan over high heat (or griddle or skillet if using the option of making the panini in either, instruction in text, above.)
Lay out the bottom slices of bread. Spread each slice with 1/4 of the mayonnaise, add 1/4 of the caramelized onions, 1/4 of the turkey. Top the turkey with 1/4 of the roasted red bell peppers, 1/4 of the spinach artichoke dip, a little fresh basil, optional, a few spinach leaves and top each sandwich with the corresponding bread slice.
Butter the tops of all the panini, add to the press or grill buttered side down. Butter the top side and close the press or grill. Close and turn heat down to medium and continue to cook until golden brown and crunchy and spinach artichoke dip is melted.
Keywords: Artichokes, Bread, hot spinach artichoke dip, leftover turkey, panera, Sandwiches, Spinach, Turkey