The lap can be easily cut with a hand saw. And the waste between the saw cuts is removed with a chisel.
The next thing to cut would be the step.
This is usually done by chisel also.
With a very sharp chisel and chopping in the correct order, the step doesn't take that long......
If you're working with planed timbers it maybe possible to "build a jig" that may help you, but I don't know which tool you'd use with the jig......
