3) Place the frying-pan under the grill. Grill until the top is set and golden brown, about 4 minutes. Using a rubber spatula, loosen the frittata from pan and slide the frittata onto a cutting board. Cut the frittata into 12 wedges.
4) Split open each bread piece. Toast the bread on a grill pan until golden. You can also grill the bread cut side up until golden, about 1 to 2 minutes, keeping a careful watch on the bread since they can easily burn. Butter the cut sides of the toasted bread. Arrange a frittata wedge on each bottom piece of bread. Cover with the bread tops and serve.