Heat the oven to 350°F (175°C). Grease two 9-inch round cake pans and line the bottoms with parchment.

Whisk the flour, granulated sugar, baking soda, and salt together in a large bowl.

Add the lightly beaten eggs, vanilla, and undrained crushed pineapple. Stir only until the batter is evenly combined.

Divide the batter between the prepared pans and smooth the tops. Bake for 25–32 minutes, until the centers spring back lightly and a tester comes out with only a few moist crumbs.

Cool the cakes in their pans for 10 minutes, then turn them out onto wire racks. Cool completely before filling or frosting.

For the filling, whisk the reserved pineapple juice, sugar, and cornstarch in a saucepan. Add the drained pineapple and cook over medium heat, stirring constantly, for about 3–5 minutes, until thick and glossy.

Stir the optional lemon juice and butter into the hot filling. Transfer it to a bowl and cool completely.

Beat the cream cheese and butter until smooth. Beat in the vanilla, then gradually add the confectioners' sugar; mix in a small amount of milk or cream only if the frosting is too stiff.

Place one cake layer on a serving plate and spread it with the cooled pineapple filling, leaving a small border. Add the second layer, then frost the top and sides.