In the bowl of your stand mixer, add all the ingredients except for the butter.
Transfer the bowl to your mixer, and start mixing at Speed 1 until the ingredients come together, 2 to 3 minutes. Add the butter, and continue mixing until incorporated.
Increase to Speed 2 and knead, until dough is smooth and elastic, about 18 minutes.
Shape the dough into a tight ball and transfer to a well-oiled bowl. Cover the bowl and let rest in a warm place, until dough is doubled in size, 45 minutes to 1 hour.
While the dough is resting, divide the salted butter into 8 pieces, and shape into tiny balls.
Once the dough has doubled, transfer to a lightly dusted or oiled surface. Separate about ⅓ of the dough.
Divide the separated dough into 8 equal-sized pieces.
One at a time, wrap the salted butter with the dough, and pinch to seal.
Divide the remaining two-thirds of the dough into 8 equal-sized pieces.
Roll the divided dough pieces into a tight ball.
One at a time, flatten a piece of dough, and place the wrapped butter balls in the center, seam-side down.
Pinch to thoroughly seal.
Arrange the bread rolls in a tray, making sure to leave sufficient space in between to allow for rising. Cover and let rest, until doubled and fluffy, 35 to 40 minutes.
While the bread is resting, make the coffee topping. In a small bowl, add the instant coffee powder and hot water, and mix until completely dissolved. Set aside.
In a medium-sized bowl, add the butter and sugar. Whisk until thoroughly combined.
Add the egg and the coffee mixture, and whisk until thoroughly combined.
Fold in the flour, and mix until thoroughly combined.
Spoon the mixture into a piping bag or small ziplock bag. Set aside until ready to use.
Preheat the oven to 180 degrees C (fan 160 degrees C).
When the rolls are done rising, pipe the coffee topping in a spiral motion, starting from the center of each roll and working your way to the edge.
Bake in the oven for 18 minutes.
Let cool on a wire rack. Serve warm.