Grease a 16 × 12 inch (40cm x 31cm) rectangular cake pan. Preheat the oven to 360°F (180°C) and place the rack in the middle.
Make the batter
Sift the flour with the baking powder, baking soda, and salt in a bowl. Set aside.
Put the eggs, sugar, and lemon zest in a separate bowl.
Mix on high speed until it forms a light yellow foamy cream (see video).
Add the oil, vanilla, milk, and lemon juice. Mix on low speed to integrate everything.
Add the flour in three parts, Mixing a little on low speed to combine it into the egg mixture between each addition.
Bake
Pour the mixture into the cake pan and bake for between 20 to 25 minutes (depending on your oven) or until you see that the bread has reached a golden-brownish color on the surface and when you insert a toothpick in the center it comes out completely clean.
Take the cake out of the oven and place it on a rack. Let it cool for about 10 minutes and then carefully remove it and place it on the rack. Let it cool completely.
Fill & decorate
Cut the cake in half and distribute the jam on top of one of the halves covering it very well.
Carefully place the other half of the cake on top and press a little to stick them to each other.
*If you are going to decorate Cortadillos with two different colors of icing, the next step is to cut the cake in two again*.
Place the confectioner’s sugar in a bowl, and add the milk and the two tablespoons of butter. Whisk until the ingredients are combined.
Add the food colorant one drop at a time and mix very well to integrate it until the desired degree of color is achieved.
Add the icing on the surface of the cake and with a spatula distribute it very well to cover it nicely.
Sprinkle with the colored sprinkles on top and let the cake sit for 30-40 minutes.
After the resting time and when you see that the glaze has completely dried, cut the cake into squares or triangles and serve.
Notes
Make sure that all the ingredients are at room temperature before you start baking.
Don't overmix the batter, overmixing can cause the cake to be tough and dense.
Don't open the oven door in the first 30 minutes when baking the cake.
Use a kitchen scale for best results.
Let the frosting dry completely before cutting the cortadillos, so the cut is even and clean.