Cutting lap joints by hand takes a little while if you are as slow as I am. To cut just one half of a lap joint took me....well, let's just say that if I were to charge $30/hour for my time, this joint alone would cost $5 million.
There are a number of ways to cut this joint, and other ways to speed up the process, but here is one way to do it:
Layout the cut with a bevel-edged pencil, marking knife or exacto blade. Use a chisel to define the shoulder. Handsa
w kerfs within the waste area. The more kerfs you saw, the easier it is to chip out the waste. My kerf marks are rather far apart because I get tired pretty quickly with handsawing. Use a beefy chisel to chip out the majority of waste then clean up the bed with a router plane or paring chisel. Because this is a wide lap joint, remove the waste from only half of the joint at a time and leave a section of wood in the middle to support your router plane as you clean up the bed. Remove the center waste section with a chisel and/or plane.Now it's onto the next one!