Preheat your oven to 350°F (175°C). Line the bottoms of three 8-inch round cake pans with parchment paper and set them aside.

In a large mixing bowl, sift together the cake flour, baking powder, and salt.

In a separate smaller bowl, whisk together the ube extract, vegetable oil, and milk. Set aside.

In another large bowl, using a handheld electric mixer, beat the egg yolks while gradually adding ⅓ cup of sugar, one teaspoon at a time. Continue beating on medium-high speed until the mixture becomes pale and thick, about 7 minutes.

Add the ube jam to the yolk mixture and beat until smooth, ensuring there are no large lumps remaining. If you'd like a more intense purple color, add a small amount of purple gel food coloring at this stage and stir until evenly blended.

To combine the wet and dry mixtures, gently fold in one-third of the flour mixture into the egg yolk mixture just until incorporated. Then add half of the milk mixture, followed by another third of the flour, the remaining milk, and finally the last third of the flour. Fold gently after each addition, being careful not to overmix the batter.

In a clean, dry mixing bowl (using a stand mixer with a whisk attachment or clean beaters on a handheld mixer), beat the egg whites on medium speed until foamy.

Add the cream of tartar and continue beating until the mixture becomes very frothy.

Gradually add the ¾ cup of sugar, one heaping teaspoon at a time, and continue beating until stiff peaks form.

To lighten the batter, take about one cup of the meringue and fold it gently into the cake batter. Then fold in the remaining meringue in two or three additions until the mixture is smooth and fully combined, taking care not to deflate the batter.

Evenly divide the batter between the prepared cake pans and smooth the tops.

Bake for approximately 20 minutes or until a toothpick inserted in the center comes out with a few moist crumbs.

Once baked, invert the pans onto a wire rack and allow the cakes to cool completely upside down. This helps maintain their height and prevents collapsing.

Refer to a basic Swiss meringue buttercream recipe to prepare the base. Once your buttercream is smooth and fluffy, begin adding ube extract ¼ teaspoon at a time, tasting as you go. Typically, about 3 teaspoons total will provide a rich ube flavor.

Continue whipping the buttercream until the flavor is fully incorporated and the color is uniform. Adjust the extract amount to suit your taste.

Once your cake layers have cooled completely, trim the tops if they are domed to ensure flat, even layers. You can also trim the sides to remove the browned edges and reveal the vibrant purple interior.

Fill and frost the cake with the ube Swiss meringue buttercream, decorating as desired. You can smooth the frosting for a clean finish or pipe designs for a more decorative look.

Chill the cake slightly before serving for cleaner slices and enhanced flavor.