Cut the ¾ cup of butter into small cubes and place in microwavable bowl. Microwave in 30-second increments, stirring in between, until butter is completely melted.
Whisk the instant coffee into the melted butter while it is still hot. You will see some granules in the butter, so let the mixture rest a minute or two, then whisk again. The melted butter should turn darker now.
Transfer the butter mixture into a medium mixing bowl and whisk in the white and brown sugars. Then whisk in vanilla extract.
Add the eggs, one at a time, whisking briskly in between additions until batter is thickened.
In a different, smaller bowl, whisk together the flour and spice mixture until incorporated.
Using a spatula, gradually fold the dry ingredients into the wet with short, quick strokes until all ingredients are combined. Do not overmix.
Pour batter into prepared baking dish and place in oven. Bake 35-40 mins, or until toothpick inserted into the center comes out clean. Remove pan to cool on wire rack.