Combine diced mango, 2 tbsp sugar, and lime juice in a blender or food processor. Blend until completely smooth. Taste and add more sugar if needed. Set aside in the refrigerator to chill thoroughly.

Halve the passionfruits and scoop the pulp and seeds into a small saucepan. Add 1/4 cup sugar and 1 tbsp water.

Heat over medium-low heat, stirring occasionally, for 3-5 minutes, until the sugar dissolves and the mixture slightly thickens. Do not boil vigorously.

Remove from heat. Keep half of the mixture with seeds for texture, and strain the other half through a fine-mesh sieve into a separate bowl to remove seeds, pressing gently with a spoon. Combine both portions (strained and unstrained) for a mix of smooth and seedy texture. Set aside to cool completely, then refrigerate until thoroughly chilled.

In a medium saucepan, combine heavy cream, whole milk, 3/4 cup sugar, and salt. Heat over medium heat, stirring occasionally, until the sugar dissolves and the mixture just begins to simmer around the edges (do not boil). Remove from heat.

In a separate medium bowl, whisk the egg yolks until light yellow and slightly thickened.

Slowly temper the egg yolks by gradually whisking about 1/2 cup of the hot cream mixture into the yolks. This prevents the eggs from scrambling.

Pour the tempered egg yolk mixture back into the saucepan with the remaining hot cream.

Return the saucepan to medium-low heat. Cook, stirring constantly with a rubber spatula, until the custard thickens enough to coat the back of the spatula (about 5-8 minutes). Do not let it boil. The temperature should reach 170-175°F (77-79°C).

Remove from heat and stir in the vanilla extract.

Pour the custard base through a fine-mesh sieve into a clean bowl to remove any potential cooked egg bits, ensuring a perfectly smooth texture.

Cover the bowl tightly with plastic wrap, pressing it directly onto the surface of the custard to prevent a skin from forming.

Refrigerate for at least 4 hours, or preferably overnight, until thoroughly chilled. This step is crucial for the ice cream to churn properly.

Once the custard base is thoroughly chilled, pour it into your ice cream maker bowl and churn according to the manufacturer's instructions (typically 20-30 minutes), until it reaches the consistency of soft-serve ice cream.

While the ice cream is churning, ensure your mango puree and passionfruit swirl are also thoroughly chilled.

Transfer about one-third of the churned ice cream to a freezer-safe container. Drizzle generously with some of the chilled mango puree and passionfruit swirl.

Repeat with another third of ice cream, then more puree and swirl, then the remaining ice cream, and finish with drizzles of puree and swirl. Gently swirl with a knife or spoon for a marbled effect, being careful not to overmix, which could dull the distinct fruit flavors.

Cover the container tightly and freeze for at least 4-6 hours, or until firm, before serving.