Preheat a fan-forced oven to 160C (320F) or 180C (356F) for a conventional oven. Line a cupcake tin with cupcake liners.
Take 2 tbsp of the milk for the batter and add to a small mixing bowl. Add the instant coffee powder and mix. Microwave for 15 seconds. Set aside to cool.
In the bowl of a stand mixer fitted with the paddle attachment, add the flour, baking powder, caster sugar and salt. Turn mixer on low speed and allow it to mix for a couple minutes to help everything combine well (alternatively you may do this by sifting the ingredients together). Add the softened butter and let it mix until it resembles a fine sand like texture.
Next, add milk, eggs, yogurt, sweetened condensed milk, oil and vanilla extract in a large jug and whisk well.
Add wet ingredients to dry ingredients in a slow and steady stream until no dry ingredients are visible. Scrape down the bowl and mix for another 20 seconds.
Add ½ of the batter into a second bowl and add the coffee. Fold in until well combined.
Add the coffee and vanilla batter into two separate piping bags. Pipe some coffee batter on the inside of the cupcake liners. Pipe it kind of in a messy zig zag. Then add some vanilla batter finished with some more coffee batter on top. You want to fill these cupcakes just above the half way point.
Bake for 30-35 min or until a toothpick inserted comes out clean. Allow them to cool completely on a wire cooling rack before frosting.
To prepare frosting mix water and coffee together. Microwave to melt everything and allow to cool down.
Split frosting into 4 bowls. Add 1 tsp coffee to one bowl and mix until well combined. Add 1 tbsp of coffee into the second and mix. Add 3 tbsp coffee into the third and mix. Fit the end of 4 piping bags with a Wilton 1M tip. I know you probably don’t have 4 of those tips lying around. But you can pipe each layer, then take the tip out and swap it into another bag for the next shade of coffee. Time consuming, but beauty knows no pain.
Core the centre of each cupcake and fill with sweetened condensed milk. The milk will soak into the cake after about 20 min so it won’t create a mess when you bite into it.
Frost the cupcakes in a single swirl starting with the dark coffee frosting and work your way up to the white frosting. Finish off with a dusting of instant coffee powder (optional)