Place the chocolate onto 2 slices of bread, and cover with the remaining bread slices. The chocolate should fit neatly inside the bread and not stick out at the edges. Butter the outsides of each sandwich and place on wax paper. Heat a grill pan or frying pan and cook the buttered sandwiches on one side until dark golden; flip and cook for the same amount of time on the other side. Press the sandwich gently with a spatula while it cooks to join the chocolate and bread together. The chocolate should be soft but not liquid.
Transfer to a cutting board and cut each sandwich into two triangles. Place, overlapping, on a dessert plate. Put a scoop of ice cream on the plate and either drizzle the raspberry coulis over the ice cream or pour a pool of it on one side of the plate.