The completion of complex activities of daily living (ADL) like meal preparation is a key concept for achieving autonomous living. Due to cognitive impairments, some people need to be supported when performing ADL. In this paper, we present a technological approach to guide people with cognitive impairments to complete complex activities. The assistance is provided in the form of pervasive human-machine interactions (HMI), that encourage the person to complete some actions to settle the difficulty identified by the system. These HMI are called "acts of assistance". This approach was implemented in Archipel, a cognitive orthosis developed at the DOMUS Laboratory, University of Sherbrooke (Canada). An evaluation of the prototype was conducted around meal preparation activities, involving 12 people with intellectual disabilities. This study demonstrates that our approach is promising