Often folks want to add a bit of style to their roof line by adding another roof pitch to the equation, called a witches hat roof, it incorporates a witches hat rafter (also called a broke back rafter) to achieve this look.
This example uses an LVL spline and some pegs to hold the two rafters together. Then a couple of structural screws, such as Rothoblass, ASSY, GRK RSS Screw to hold the rafters to the plates. The bottom rafter is then housed into the plate 1″ so the weight of the rafter bears on it and not the top of the plate.
Would this be appropriate for a lean-to rafter connection?
Yes, but you would not need to use the LVL, just screw the two rafters to the plate instead. The LVL, in this case, supports the roof overhang.