Preheat oven to 350°F/175°C. Line four 7-inch pans, or three 8-inch round pans with parchment rounds, and grease with non-stick cooking spray.
Mix together all dry ingredients (3 cups (375g) flour, 2 1/2 cups (500g) granulated sugar, 2 1/2 tsp baking powder, and 1 tsp fine salt) in a stand mixer with a paddle until fully combined.
Mix in 1 cup of room-temperature butter slowly into the dry mix, on a low speed. Continue to mix until no large chunks of butter remain, and the mixture becomes crumbly.
Pour in 1 cup (240g) of egg whites, and mix on low until just incorporated. Mix in 1 1/2 cups (360g) of whole milk in two installments, on a low speed.
Add in 2 Tbsp oil, 2 tsp vanilla extract, and 2 tsp rose water. Mix at a low speed until fully incorporated.
Scrape down the sides of the bowl with a spatula, then beat on low speed for about 15 seconds (the key is to mix until the ingredients are JUST incorporated, so that the batter isn't overmixed).
If desired, add a couple of drops of pink or red gel food coloring. Mix the color in by hand using a rubber spatula, scraping the sides and bottom of the bowl partway through. Mix until the batter is evenly colored.
Divide batter evenly between the prepared cake pans (about 450 grams per pan if you use 4 pans, or 600g if you use three pans). Bake for 34-36 minutes, or until a toothpick comes out clean. Let the pans cool for 10 minutes, then run an offset spatula around the perimeter of the pan to separate the cake from the pan.
Place cake layers into the freezer for 45 minutes to accelerate the cooling process. Once the layers are fully cooled, carefully flip the pans and remove the layers from the pans. Use a serrated knife to level the tops of the layers.