Preheat oven to 350 degrees F. Prepare a 9 X 5 X 5 loaf pan with nonstick cooking spray. Set aside.
Mix all cake ingredients together in a large mixing bowl.
Using a hand mixer, or a stand mixer fitted with the paddle attachment, beat for 2 minutes.
Pour batter into loaf pan until 2/3 full. If you have extra batter, you can prepare a few mini-loaf pans with nonstick spray and bake the additional batter in those pans.
Bake for 40-45 minutes or until a cake tester inserted in the center comes out clean. If also making mini-loafs, they should be ready in 25-30 minutes.
Remove pans from oven and cool completely on a cooling rack. When cooled, wrap tightly in plastic wrap and place in freezer. This will make the cake easier to slice later.
Place milk in a small sauce pan, and whisk in flour until flour is incorporated into milk keep whisking as to avoid getting lumpy.
Slowly heat the milk and flour over low heat, and whisk continuously to ensure mixture is smooth.
Continue to mix until mixture is a pudding-like consistency. Remove from heat and transfer to a small glass bowl. Cover with plastic wrap and refrigerate until cold. (You can also prepare this the day before you plan to make the cake).
Place softened butter and sugar in a medium bowl, or the bowl of a stand mixer fitted with the whisk attachment. Blend until light and fluffy. Add milk/flour mixture and continue to beat until fluffy and thick. This may take up to 5 minutes.
Place chopped chocolate and coffee granules in a bowl. Over low heat, in a small saucepan, heat cream until it starts to boil. Switch off heat, and pour over chocolate, whisking until chocolate melts and become smooth.
Add vanilla and milk/flour mixture and beat until the filling is light and fluffy!! This may take a lot of mixing. I put it in my stand mixer and whip for about 5 minutes.
Slice loaf horizontally into 3 equal-size loafs.
Place bottom layer on a cake plat, and frost top with 1/3-1/2 cup of filling. Repeat with the next two layers, pressing each layer down slightly. Filling may squeeze out of the side, so use a knife to smooth it out, or remove excess filling.
After the top layer is placed, frost with the ganache, allowing excess to drip over the sides.