Preheat the oven to 350°F and grease a 9-inch springform pan. For the cherry marble cake, pour the flour, melted butter, sugar, baking powder, milk, salt, and eggs into the large jar. Screw on the lid and shake the jar for about 2 minutes until a smooth batter forms. If you'd prefer to make the cake batter in a more traditional way, you can also combine the ingredients using a hand mixer. Pour half of the batter into the springform pan.
Add 2 tablespoons of milk and 2 tablespoons of cocoa powder to the remaining batter in the jar, close the jar, and shake it vigorously until a smooth batter forms. Pour the chocolate batter into the springform pan and use a toothpick to create a marble pattern in the cake batter.
Press the maraschino cherries into the batter. Transfer the springform pan to the oven and bake the cherry marble cake at 350°F for 45 minutes. Once it has baked, take the marble cake out of the oven and let it cool. Heat up the cherry preserves and brush a thin layer of it on top of the marble cake.
Sprinkle the hazelnuts on top of the layer of cherry preserves while it's still warm.
Remove the ring from the springform pan and place it on top of a piece of parchment paper. Temper the chocolate chips, pour the tempered chocolate into the ring of the springform pan, and spread it around evenly.
Remove the ring of the springform pan and let the chocolate set. Once it has hardened, carefully remove the round piece of chocolate from the parchment paper and place it on top of the hazelnuts on the marble cake. Melt the hardened chocolate with a hair dryer or culinary torch so that the chocolate coats the hazelnuts and marble cake evenly.
