Bake the cake: In a large mixing bowl, mix together the flour, sugar, baking soda and salt. In a separate bowl, dissolve the instant coffee in the hot water. Then add the cocoa powder and vanilla extract, whisk together, then pour into the dry mixture. Add the vegetable oil, chocolate chips and vinegar, and mix until everything is well combined. Pour into a greased 9-inch round cake pan and bake at 375F for 30-35 minutes. Let cool in the pan for 10 minutes, then transfer to a wire rack and cool completely.
Assemble the cake pops: Weigh 375 grams of chocolate cake and break apart into fine crumbs. In a separate bowl, combine the 100 grams melted chocolate chips and whipping cream, then pour into the cake crumbs and mix well. Shape into 15 balls and make a crater shape in the center of each. Place in the freezer for 15-20 minutes, until very firm. Reshape the cake pops so the edges are smoother and more defined. Return to the freezer for 5 minutes.
Dip the lollipop sticks in the 300 grams melted chocolate chips and stick one lollipop stick into the bottom of each cake pop. Place in the fridge for 15-20 minutes, until the chocolate has set. Dunk the cake pops into the melted chocolate and stick into a tall container and transfer to the fridge for the chocolate coating to set, 15-20 minutes.
Spread some Nutella onto the inside of the crater and stick the crushed rock candy into the crater to create a geode. Placing the darker colors in the center and the lighter on the outside will create depth. Enjoy your sparkly cake pops!