Preheat the oven to 180C/350F. Grease two 8-inch cake pans and set aside.
In a mixing bowl, whisk together the flour, sugar, salt, and baking soda. Add the vinegar, oil, vanilla extract, and water, and mix until smooth. Divide the batter into two bowls. Add yellow food coloring to one and red food coloring to the other.
Transfer the two cake batters into the cake pans and bake for 25-27 minutes, or until a skewer comes out clean.
Remove the cakes from the oven and let them cool completely. Once cool, carefully slice the cakes lengthways to leave four thin cake layers.
To make the frosting, add the powdered sugar and butter into a bowl of a stand mixer. On low speed, beat together until smooth and creamy. Add the vanilla extract and gently add the heavy whipping cream until combined.
Divide the frosting into two bowls. In one of them, stir through the red food coloring.
Assemble the cake. Add a single red layer to a flat surface. Spread with some of the plain frosting. Add a yellow layer on top and add more frosting. Repeat the process until the final layer of cake is placed on top. Once layered, use the red frosting to frost the top of the cake and the exterior.
Let the cake sit for several minutes, before slicing and serving.
Notes
TO STORE: Leftovers are best to be stored in the refrigerator, covered, for up to one week. Let the cake sit at room temperature for 30 minutes before serving. TO FREEZE: Place the frosted cake in an airtight container and store it in the freezer for up to 6 months.