Preheat your oven to 350°F. Grab a 10x15x1-inch baking sheet, also known as a jelly roll pan, and line it with parchment paper. This will help the cake come out easily later.
In a small mixing bowl, combine ¾ cup all-purpose flour, 1 teaspoon baking powder, and ½ teaspoon salt. Whisk them together to ensure even distribution of the leavening agent.
In a separate large mixing bowl, use a stand mixer or a handheld mixer to beat together 4 large eggs, ½ cup granulated sugar, 3 tablespoons vegetable oil, 1½ teaspoons pure vanilla extract, and ½ teaspoon pure almond extract. Beat this mixture on high speed for about 5 to 6 minutes until it becomes thick and light yellow in color.
Gently fold the flour mixture into the wet ingredients until just combined. Be careful not to overmix, as you want to retain the air bubbles that were created.
Divide the batter evenly among six bowls, aiming for about ⅔ cup in each. Use the gel food coloring to tint each bowl a different color; start with red, then orange, yellow, green, blue, and purple. The amount of coloring depends on how vibrant you want the shades to be.
Transfer each color into six disposable piping bags or quart-size ziplock bags and secure the tops. This will make it easy to pipe the colors onto your baking sheet.
Lightly spray the prepared baking sheet with nonstick spray. Snip a small corner off each piping bag, and begin piping the batter onto the sheet. Start with the red batter and make a straight line, followed by orange, yellow, green, blue, and purple. Continue until the pan is filled with colorful lines.
After piping, gently tap the pan on the counter to release any trapped air bubbles. Bake the cake in the preheated oven for about 8 minutes or until the edges start to slightly pull away from the sides.
Once baked, remove the pan from the oven. Dust the baked cake with powdered sugar, which will prevent it from sticking when you roll it.
Prepare a large cutting board or cooling rack. While the cake is still warm, place a clean piece of parchment paper over the top and flip it onto the board or rack. Remove the original parchment paper gently.
Fold the overhanging parchment paper up over the cake and start rolling it from one short side to the other, keeping the parchment inside the roll. This helps maintain its shape. Set the rolled cake aside on a cooling rack.
In a mixing bowl, beat ¾ cup salted sweet cream butter for about 1 to 1½ minutes until it’s smooth. Add 1 teaspoon clear vanilla flavoring and ½ teaspoon almond extract, mixing for another 30 seconds.
Gradually add 2 cups powdered sugar, alternating with 2 tablespoons heavy cream, beating until smooth. This creamy filling will complement the cake perfectly.
Once the cake has completely cooled, gently unroll it. Spread the filling over the surface, avoiding the edges. Be generous but careful.
Prepare two sheets of plastic wrap, overlapping them slightly and spraying with nonstick spray. Carefully roll the cake back up, wrapping it tightly in the plastic once rolled. Chill in the refrigerator for about 6 hours to set.
When you’re ready to serve, carefully unwrap the cake and slice it into ten ½-inch pieces.