01 - Preheat oven to 350°F. Line bottom of 9-inch springform pan with parchment paper.
02 - Beat eggs and sugar with electric mixer until pale and tripled in volume (about 5 minutes). Gently fold in flour, salt, and vanilla extract until just combined. Pour into pan and bake for 12–15 minutes until toothpick inserted in center comes out clean. Cool completely in pan.
03 - Sprinkle gelatin over 3 tbsp cold water and let bloom for 5 minutes. Gently heat bloomed gelatin until dissolved (do not boil). Blend mango puree, sugar, and lemon juice until smooth. Stir in dissolved gelatin. Whip heavy cream to soft peaks and gently fold into mango mixture until smooth.
04 - Pour mousse over cooled sponge base, smoothing top. Refrigerate for at least 2 hours until set.
05 - Bloom gelatin in 2 tbsp cold water. Gently heat until dissolved. Mix mango puree, lemon juice, and sugar in bowl, then stir in dissolved gelatin. Let cool to room temperature, then pour over set mousse layer.
06 - Chill for at least 2 more hours until glaze is firm. Carefully run knife around edge of pan and remove cake. Decorate with fresh mango slices and mint leaves if desired. Slice and serve chilled.