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 until just combined. Pour into pan and bake 12-15 minutes until toothpick inserted comes out clean. Cool completely in pan.
03 - Sprinkle gelatin over 3 tbsp cold water, let bloom 5 minutes. Gently heat until dissolved without boiling. Blend mango puree, sugar, and lemon juice until smooth. Stir in dissolved gelatin. Whip heavy cream to soft peaks and fold into mango mixture until smooth.
04 - Pour mousse over cooled sponge base, smoothing top. Refrigerate at least 2 hours until set.
05 - Bloom gelatin in 2 tbsp cold water. Heat until dissolved. Mix mango puree, lemon juice, and sugar, then stir in dissolved gelatin. Cool to room temperature, then pour over set mousse layer.
06 - Chill at least 2 more hours until glaze is firm. Run knife around edge of pan and remove cake. Decorate with fresh mango slices and mint leaves if desired. Slice and serve chilled.