Preheat the oven to 350°F. Spray two 9-inch round cake pans with baking spray (or grease with butter/oil) and line the bottoms with parchment rounds. Set the prepared pans aside.

In a large mixing bowl, combine 1 1/4 cups granulated sugar, 3/4 cup light brown sugar, 1 cup sour cream, 1/2 cup canola oil, 3 large eggs (room temperature), and 2 teaspoons vanilla extract. Using a handheld mixer on medium speed, beat until the ingredients are fully combined and the mixture is smooth (about 1–2 minutes). Scrape down the bowl as needed.

In a separate bowl, whisk together 2 cups all-purpose flour, 3/4 cup unsweetened cocoa powder (sifted), 2 teaspoons baking powder, 1/2 teaspoon baking soda, and 1/2 teaspoon salt until evenly distributed.

In a small bowl, dissolve 1 tablespoon instant coffee granules in 1 cup hot water; stir until the granules are fully dissolved.

Add half of the flour-cocoa mixture to the bowl with the wet ingredients and beat just until incorporated. Add the coffee mixture and beat just until incorporated. Add the remaining flour-cocoa mixture and beat for 1–2 minutes more, until the batter is smooth and uniform. Scrape the sides and bottom of the bowl to ensure everything is mixed.

Divide the batter evenly between the two prepared 9-inch pans, smoothing the tops with a spatula. Tap the pans gently on the counter to release large air bubbles.

Bake for 30–35 minutes, or until a toothpick inserted into the center of each cake comes out clean or with a few moist crumbs. Remove the pans from the oven and let the cakes cool in the pans for 10–15 minutes.

After 10–15 minutes, run a knife around the edges, invert the cakes onto a wire rack, remove the parchment rounds from the bottoms, and allow the cakes to cool completely before frosting.

To make the fudge frosting, place 1 1/2 cups unsalted butter (room temperature) in a large mixing bowl or the bowl of a stand mixer fitted with the whisk attachment. Whisk on medium-high speed until the butter is smooth and fluffy (about 1–2 minutes).

With the mixer on low speed, add 6 cups sifted powdered sugar and 1 cup sifted unsweetened cocoa powder. Start slow to prevent powdered sugar from dusting the kitchen, then increase to medium and mix until the mixture is thick and smooth.

While the mixer is running, slowly add 3/4 cup heavy cream and 2 teaspoons vanilla extract. Mix until fully combined. Scrape down the sides and bottom of the bowl, then whisk on medium-high speed for an additional 2–3 minutes, until the frosting is light, fluffy, and smooth. The frosting should be thick enough to hold its shape but still spreadable.

Place one cooled cake layer on a serving plate or cake stand. If the layer has a dome, level it with a large serrated knife. Spread approximately one-third of the fudge frosting evenly over the top of this layer, reaching to the edges.

Place the second cake layer on top (level it first if needed). Use the remaining frosting to cover the top and sides of the cake, spreading evenly. Smooth the frosting as desired, then slice and serve.