Preheat oven to 350°F. Spray 2, 8-inch round cake pans with nonstick cooking spray and line each with parchment paper. Set aside.
To a medium saucepan over medium heat, add butter. Once the butter has melted, add the instant coffee and hot water. Remove from heat. Whisk until fully combined. Set aside.
To a large bowl, add flour, sugar, salt, and baking soda. Add the butter mixture. Stir to fully combine.
To a separate bowl, add buttermilk, eggs, and vanilla. Stir to combine. Pour over the batter, whisking until well combined.
Evenly divide the batter between the two prepared cake pans.
Bake for 24-26 minutes, or until a toothpick comes out mostly clean.
Let the cakes cool to room temperature. Once cool, cut each cake layer horizontally into two layers, creating a total of 4 layers.
Place the layers onto a lined baking sheet and transfer to the freezer for at least 2 hours, up to overnight.