Preheat your oven to 350 degrees F (180 degrees C). Grease a 9 inch loaf pan. Line the bottom of the pan with parchment paper.
Melt chocolate in a double boiler (see here). Add steeped coffee to it and mix nicely. Set aside to cool down.
With a hand blender whip butter and sugar until light and fluffy in texture. Add vanilla extract and one egg at a time, each time whip the batter for 1 – 2 minute.
Sift flour, baking powder and salt in a separate bowl.
Now in the butter mixture add flour and yoghurt alternately in three additions and mix with the spatula gently each time so that all combined and moistened well.
Divide batter into two equal parts in separate bowls.
Mix in melted chocolate in one part of a batter and mix well to combine nicely.
In loaf tin, add a spoonful of vanilla batter on one side of the tin. Adjacent to it add spoonful of chocolate batter and then next to it vanilla batter.
Similarly, arrange spoonfuls of batter alternatively in the whole tin
Once the batter is arranged with a wooden skewer swirl to make a design but do not swirl too much as marble effect will not come neat.
Bake in preheated oven for 55 minutes or until the toothpick inserted comes out clean. Once done remove from oven and cool on a wire rack.
To make glaze, heat cream in a pan with butter, add hot cream over chopped chocolate and mix nicely until chocolate melted nicely.
Cool the glaze and with the help of fork spread evenly over marble loaf.
Cut into slices and serve.