Salted Butter (120 gram) and Semi-Sweet Chocolate Chips (120 gram) in double boiler. Set aside.
Separate Egg (4) Yolks and Whites, and set aside.
Whisk Egg Whites from medium to high speed until stiff peaks form.
Beat Egg Yolks, Vanilla Extract (1 teaspoon) and Brown Sugar (90 gram) at medium speed in another mixing bowl till thick and fluffy. Slowly pour yolk mixture into egg white, beating at low speed. Add melted chocolate and mix well.
Sift All-Purpose Flour (140 gram), Unsweetened Cocoa Powder (2 tablespoon), Baking Soda (1 teaspoon) in 3 batches and fold well with a rubber spatula. Add Natural Unflavored Yogurt (100 gram) and Rum (1 tablespoon), mixing well.
Pour chocolate batter into a 11 x 7.5 inch cake pan lined with parchment paper at the bottom and sides.
Mix All-Purpose Flour (45 gram), Unsweetened Cocoa Powder (2 tablespoon), Raw Sugar (30 gram) and Salted Butter (30 gram) with finger tips into crumbles. Sprinkle evenly over batter.
Bake in preheated oven at 170 degrees C (340 degrees F) for about 40 minutes.
Leave the cake to cool in pan, remove from mold and cut into pieces. Decorate as desired. Enjoy!