In a large mixing bowl, combine the granulated sugar and orange zest. Rub together with your fingertips until fragrant.
Add the butter and brown sugar. Beat until light and fluffy, about 2 to 3 minutes.
Beat in the egg, egg yolk, vanilla extract, and orange extract if using.
In a separate bowl, whisk together the flour, cocoa powder, cornstarch, baking powder, baking soda, salt, and espresso powder.
Gradually add the dry ingredients to the wet ingredients and mix just until combined.
Cover the dough and refrigerate for 30 minutes.
Preheat the oven to 350°F (175°C). Line two baking sheets with parchment paper.
Scoop 30-gram portions of dough (about 2 tablespoons each) and roll into balls.
Place the dough balls 2 inches apart on the prepared baking sheets.
Use the back of a rounded teaspoon to create deep indentations in the center of each cookie.
Bake for 10 to 12 minutes, until the edges are set and the centers remain slightly soft.
Immediately re-press the indentations while the cookies are warm if needed.
Cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely.
Spoon about 1 teaspoon of orange marmalade into each cookie center.
Combine the chocolate chips and coconut oil in a microwave-safe bowl. Heat in 20-second intervals, stirring between each interval, until smooth.
Drizzle the melted chocolate over the cookies.
Garnish with additional orange zest if desired.
Allow the chocolate to set before serving.