This cake looks amazing! That frosting is truly making me drool right now

This recipe works best if you make the coffee fudge in advance. The recipe will make more than what's needed for the frosting technique in the photos; if you want to use it all though, you can go for a drippy cake look or an overall glaze. The fudge also keeps in the refrigerator for up to 2 weeks; you can use it for other desserts, like your post-dinner ice cream sundae

Ingredients:
Special Equipment:
a rotating cake stand (see baker's notes)
an offset spatula

For the Coffee Fudge:
(makes 2/3 cup)
3 tablespoons strong (preferably cold brew) coffee
2 tablespoons unsweetened cocoa powder
1-ounce dark (at least 70% cacao) chocolate, roughly chopped
a pinch of kosher salt
1/4 cup (2 fluid ounces) heavy cream
2 tablespoons granulated sugar
2 tablespoons light corn syrup

For the Coffee Cake:
(makes an 8-inch, two-layer cake)
2 1/2 cups (11.25 ounces) all-purpose flour
1 tablespoon instant coffee powder
1 1/2 teaspoons baking powder
1 teaspoon baking soda
1 teaspoon kosher salt
1 3/4 cup (12.25 ounces) granulated sugar
2 large eggs
1 tablespoon pure vanilla extract
1 cup (8 ounces) sour cream
1/2 cup (4 fluid ounces) canola oil
3/4 cup (6 fluid ounces) strong (preferably cold brew) coffee, at room temperature

For the Sweetened Condensed Milk Frosting:
(makes enough for an 8-inch, two-layer cake)
1 1/2 cups (3 sticks // 12 ounces) unsalted butter, at room temperature
1 teaspoon pure vanilla extract
a pinch of kosher salt
4 1/2 cups (18 ounces) confectioner's sugar
6 tablespoons sweetened condensed milk

Recipes:

For the Coffee Fudge:In a medium bowl, combine 3 tablespoons coffee, 2 tablespoons unsweetened cocoa powder, 1 ounce roughly chopped dark (at least 70% cacao) chocolate and a pinch of kosher salt. Whisk to combine and set aside.
In a heavy-bottomed saucepan over medium-high heat, combine 1/4 cup heavy cream, 2 tablespoons granulated sugar, and 2 tablespoons light corn syrup. Stir intermittently while bringing to a boil; the moment it boils, immediately pours it into the bowl containing the chocolate and coffee (from the 1st step). Let sit for 1 full minute undisturbed.
After a minute, slowly begin to whisk the mixture. Continue whisking until the mixture is glossy and silky smooth, speeding up your whisking. This will take around 2 to 4 minutes depending on your speed and strength. Transfer to a small glass jar with a lid to cool to room temperature. Store in the refrigerator for up to 2 weeks; do not freeze.

For the Coffee Cake:Center a rack in the oven and preheat to 350 (F). Prepare two 8-inch round cake pans by spraying generously with cooking spray and lining the bottoms of each with a parchment paper circle; spray the paper as well.
In a medium bowl, combine 2 1/2 cups all-purpose flour, 1 tablespoon instant coffee powder, 1 1/2 teaspoons baking powder, 1 teaspoon baking soda, and 1 teaspoon kosher salt. Whisk to combine and set aside.
In the bowl of a freestanding electric mixer fitted with a paddle attachment, combine 1 3/4 cup granulated sugar, 2 large eggs, and 1 tablespoon pure vanilla extract. Beat on medium speed for 3 minutes, or until light and fluffy. Reduce the speed to its lowest setting and add 1 cup sour cream, beating until incorporated. With the mixer still on its lowest setting, slowly pour in 1/2 cup canola oil and continue beating until incorporated. Once the oil is incorporated, slowly pour in 3/4 cup coffee and continue beating until combined.

Stop the mixer and scrape down the bottom and sides of the bowl. Turn on the mixer back to its lowest setting and add the dry ingredients (from the 2nd step) a few big spoonfuls at a time, beating on low speed until the dry ingredients have just disappeared into the batter.
Divide the cake batter between the two prepped pans and transfer to the preheated oven. Bake for 30 to 35 minutes, or until the top of the cakes are golden and bounce back when gently poked. Transfer to a wire rack to cool for 20 minutes, before turning out onto the rack to cool completely to room temperature.

For the Sweetened Condensed Milk Frosting:In the bowl of a freestanding electric mixer fitted with a paddle attachment, beat 1 1/2 cups unsalted butter, 1 teaspoon pure vanilla extract, and a pinch of kosher salt at medium speed until soft and fluffy. Lower the mixer speed to its lowest setting and add 4 1/2 cups confectioner's sugar, turning the mixer speed back up to medium once the sugar is fully incorporated. Beat for 2 to 3 minutes until light and fluffy, and reduce the mixer speed back down to its lowest setting. Drizzle in 6 tablespoons sweetened condensed milk; once the milk has been added, turn the mixer back up to medium and beat for another 2 to 3 minutes until light and fluffy. Use immediately.

source here