In a small bowl, add oil, butter and condensed milk. Whisk until blended smoothly.
Add in the powdered sugar. Whisk again.
In a small separate bowl, mix together the milk, vinegar and vanilla extract. Keep it aside for 5 to 10 minutes.
In a large bowl, add in the flour, baking soda, baking powder and mix them together. This will serve as your mixing bowl
Add the wet ingredients from the small bowls into the dry ingredients. Mix everything till combined to the consistency as shown in the video.
Split the batter into 2 equal parts and use gel coloring, blue and red, one for each.
Preheat the oven to 350 F .
Line an 8"x 8" pan with a piece of parchment paper and grease with melted butter. Since we are looking to bake a thin cake, you just need a tray that is about 1 or 2 inches deep.
Pour each colored batter into a piping bag or sandwich bags to do the piping.
Carefully pipe out 1 to 1.5 inch width of the batter and alternate between red and blue.
Bake in the preheated oven for 15 minutes.