Put the semi-sweet chocolate and oil in a large mixing bowl (microwave-safe) and microwave on high for 30 seconds and then stir. Continue to microwave in 10 second increments, stirring in between, until the chocolate is melted. If you don’t have a microwave, a double boiler will work just fine. Set aside to cool a beat.
Once the chocolate mixture is cooled a bit, whisk the eggs into the chocolate mixture, one at a time. Make sure each egg is well blended before adding in the next. Whisk in the vanilla, brown sugar and granulated sugar. This mixture will be thick…don’t panic. Grab a rubber spatula and mix in the cocoa powder, baking powder, baking soda and salt. Scrape the bottom and sides of the bowl to make sure everything is well combined. Fold in the bread flour and all-purpose flour; and finally fold in the marshmallows and dark chocolate chips (or chopped chocolate) until just combined. Cover the mixing bowl and stash in the fridge for 30 minutes to firm up a bit; the dough rests while you preheat the oven and prep your baking sheets. Preheat your oven to 375°F (190℃) and have a rack in the top third of the oven…this is where you’ll bake your cookies. Line your cookie sheets with parchment paper.
Scoop 2 tablespoons of cookie dough and allow at least 2 inches (5 cm) between the dough balls on the prepared baking sheet. Try to make them as spherical as possible. They will spread a touch while baking. If you have the time, I highly recommend either freezing these dough balls for 5 minutes or placing them in the fridge for 20 minutes prior to baking. This will keep cookie spread to a minimum. You know how I like girth in a cookie.
Bake for 11 minutes. You want to slightly undercook these…they might even look underdone a bit. That’s perfect. For best results, allow the cookies to cool on the sheet for 5-10 minutes, or until they come off easily. Then transfer to a cooling rack. Store in an airtight container at room temerpature for up to several days.