In a medium bowl, mix flour, cocoa, baking soda, salt, cinnamon, and ginger.
In the bowl of a double boiler, melt butter and water together. When butter has mostly melted, add sugar, brown sugar, molasses and chopped chocolate. Stir just until everything is melted you don’t want the butter to separate or the chocolate to get chunky, so remove the bowl from the heat when everything has melted, even if the sugar granules haven’t fully dissolved.
Off the heat, whisk in the eggs one at a time, whisking each time to incorporate. The mixture will start to look shiny. Add the dry ingredients, stirring just until they disappear. Add oats and mix just to incorporate. Scoop your cookies (by the tablespoon) onto parchment- or silicone-lined baking sheets, cover with plastic wrap and refrigerate at least 1 hour, up to several days. Bake at 350 degrees for 11-13 minutes until just done (they’ll still look quite soft when you pull them out). Use a wide spatula to transfer cookies onto a rack, and cool to room temperature.
From Not Derby Pie blog. Inspired by Dorie Greenspan’s Baking from My Home to Yours.