Add 1–2 teaspoons of cold water to the gelatin powder. Stir gently and let it bloom for 5 minutes.Meanwhile, add the lemon juice to the mango puree and heat over low heat until it starts to simmer. Turn off the heat, add the bloomed gelatin, and stir until completely dissolved.Strain the mango mixture through a fine-mesh sieve to remove any lumps and get a smooth texture.
Place the dessert glasses at an angle in a muffin pan to keep them from tipping over. Carefully pour the mango mixture into each glass, keeping the glasses tilted to create a slanted layer.Transfer the muffin pan with the glasses to the refrigerator and chill for about 30 minutes, or until the mango layer is set.
Vanilla Layer
While waiting, prepare the vanilla panna cotta. Add 1–2 teaspoons of cold water to the gelatin powder and let it bloom for 5 minutes.In a saucepan, combine the heavy cream, milk, sugar, and vanilla extract. Heat over low heat, stirring occasionally, until the mixture starts to simmer. Turn off the heat, add the bloomed gelatin, and stir until completely dissolved.
Strain the cream mixture through a fine-mesh sieve to remove any lumps. Let it cool until it is no longer hot, but still liquid.Once the mango layer has set, remove the glasses from the refrigerator and place them upright. Slowly pour the vanilla panna cotta mixture over the mango layer.Return the glasses to the refrigerator and chill for at least another 30 minutes, or until the panna cotta is set. Before serving, decorate with fresh mango cubes and mint leaves. Serve chilled.
Notes
Use ripe, sweet mangoes. Choose ripe mangoes for the best flavor and natural sweetness. I didn't add any sugar to the mango layer because my mangoes were already sweet enough. If your mangoes are slightly sour, you can add a little sugar to taste.
Bloom the gelatin properly. Always use cold water to bloom the gelatin and let it sit for about 5 minutes before adding it to the warm mixture. This helps the gelatin dissolve evenly without leaving lumps.
Turn off the heat before adding gelatin. Once the mango or cream mixture starts to simmer, turn off the heat before adding the bloomed gelatin. The remaining heat is enough to dissolve it. I've noticed that when I continue heating the mixture with gelatin, it sometimes develops an unpleasant smell. This is why I prefer adding gelatin after turning off the heat.
Let each layer set before adding the next. Chill the first layer for about 30 minutes, or until it has set. Make sure the second mixture has cooled down and is no longer hot before pouring it over the first layer. Otherwise, the heat may soften the gelatin and cause the layers to mix.
Try different ways to arrange the layers. For the slanted presentation, I use a muffin pan to hold the glasses at an angle while the mango layer sets. Once it is firm, I stand the glasses upright and gently pour in the vanilla panna cotta. You can also make the cream layer first and add the mango layer on top for a different look. Both versions are pretty, especially when topped with fresh mango cubes and mint leaves.