A cookie scoop is a great kitchen gadget for ensuring even sized cookies
If you don't have a food processer use a stick blender to mash the beans, or mash with a fork - ensuring that they are well mashed. With an electric beater beat the softened butter, brown sugar and vanilla extract until creamy. Beat in the egg. Add the mashed beans and mix well. Add the remaining ingredients and mix well.
If preferred omit scattering the chocolate on top of the cookies. Once cookies are cold, melt the remaining chocolate and drizzle over the cookies.