Dough: Preheat oven to 350F. Grease a cast iron skillet with cooking spray or canola oil. Using an electric mixer, beat oils and sugars together in a large mixing bowl until well blended. Add eggs and vanilla, beating until smooth and creamy.

In a separate bowl, whisk together flour, espresso, baking soda, and salt; add to egg mixture and beat until just blended and incorporated. Fold in the chopped chocolate.

Melt: In a separate small bowl, melt remaining chocolate in microwave in 20 second intervals, stirring in between, until melted and smooth (alternatively, chocolate can be melted in double boiler over low heat). Set aside.

Spread half the dough in bottom of prepared pan. Spread melted chocolate evenly over the dough. Cover with remaining half of dough, using a spoon or spatula to spread into an even layer.

Bake for 20-22 minutes. Cookie should be golden