The File - Recent Files command opens the project editor command for the selected project file. When you select the command, a pull right menu displays a most recently used list. Select the desired project from the list. A project editor tab is opened and displays the selected project. If an editor tab was already open for the selected project, then that editor project tab is displayed in the session window.
You may also open a recently used project by clicking on the Edit Project icon in the Sonnet task bar, then selecting the project from the list displayed in the pop-up menu which appears.