Preheat oven to 350°F (177°C). Spray a 9×5 inch loaf pan with nonstick spray.

Whisk the cake flour, baking powder, baking soda, and salt together in a large bowl. In a medium bowl, whisk the melted and slightly cooled butter, egg, granulated sugar, sour cream, milk, and vanilla together until combined. Pour the wet ingredients into the dry ingredients, then whisk to completely combine. Avoid over-mixing. Fold in the sprinkles.

Pour the batter into prepared loaf pan. Bake loaf cake for 50 minutes to 1 hour, covering loosely with foil about halfway through to prevent the top from over-browning. Poke the center of the cake with a toothpick. If it comes out clean, the cake is done. Oven times will vary between ovens. My cake usually takes 55 minutes. Cool completely in the pan set on a wire rack.

The video tutorial above is a helpful visual for the next few steps. Carefully remove cooled cake from loaf pan. (You will use the loaf pan again in the next step.) Place on a cutting board and using a very sharp or serrated knife, slowly slice horizontally into 3 even layers. As shown in the video above, I usually stand the loaf upright on one end and cut it down vertically. Feel free to use a ruler for precision. A cake leveler isn’t very helpful because this is a denser cake.

Remove ice cream from freezer. Let it soften for 15 minutes or microwave it for about 20-30 seconds.

Line loaf pan with parchment paper or plastic wrap with enough overhang on the sides to lift the ice cream loaf cake out of the pan after freezing. Place bottom loaf cake layer into lined pan. Slowly and carefully spread 1 pint of softened ice cream in an even layer on top. Top with center loaf cake layer. Slowly and carefully spread 2nd pint of ice cream evenly on top. Place top loaf cake layer on top, pressing it down gently so it really sticks to the ice cream beneath it. Cover assembled loaf cake with aluminum foil or plastic wrap and freeze for at least 8 hours and up to 3 days. (If freezing for longer than 1 day, let it sit for 10 minutes at room temperature before pouring ganache on top in step 9.)

Place chopped chocolate in a medium heat-proof bowl. Heat the cream in a small saucepan over medium heat until it begins to gently simmer. (Do not let it come to a rapid boil– that’s too hot!) Pour over chocolate, then let it sit for 2-3 minutes to gently soften the chocolate. With a metal spoon or small silicone spatula, very slowly stir until completely combined and chocolate has melted. The finer you chopped the chocolate, the quicker it will melt with the cream. Set aside for 10 minutes to thicken as you complete the next step.

Remove loaf cake from the freezer and using the parchment overhang on the sides, carefully lift it out of the loaf pan. Parchment may tear, but do your best to remove the whole cake. Use a knife to loosen it from the pan if needed. Remove parchment from cake and place cake on a cutting board.

Pour and spread ganache on top. Garnish with sprinkles if desired. Ganache will set quickly since the loaf is so cold. Let the cake sit for 3-5 minutes to slightly soften before slicing. (Slicing will be VERY hard to do otherwise!)

Using a very sharp or serrated knife, cut into slices about 3/4 inch thick. Cake will be hard since it’s frozen, but softens as the minutes go by. I like it better when the cake and ice cream are a little softer after a few minutes.

Cover and store leftover cake/slices in the freezer for up to 1 week.