Follow these straightforward steps to craft your Little Tahini and Molten Chocolate Mousse Tarts with Mascarpone:

1. Prepare the Tart Shells: In a mixing bowl, combine the flour, powdered sugar, and salt.
2. Mix in Butter: Add the softened butter and work it into the dry ingredients until crumbly. Mix in the egg yolk and cold water until a dough forms.
3. Chill the Dough: Wrap the dough in plastic wrap and refrigerate for at least 30 minutes.
4. Preheat the Oven: Preheat your oven to 350°F (175°C).
5. Roll and Shape: Roll out the chilled dough on a floured surface and cut into circles. Place the circles into tartlet pans.
6. Bake: Bake the tart shells for 10-12 minutes or until lightly golden. Allow them to cool completely.
7. Prepare the Mousse: Melt the chopped dark chocolate in a heatproof bowl set over simmering water. Stir in the tahini until smooth.
8. Combine Eggs and Sugar: In another bowl, whisk the eggs and sugar together until pale. Gradually add the melted chocolate mixture, followed by vanilla extract.
9. Fill Tart Shells: Pour the chocolate mousse into the cooled tart shells, filling them about three-quarters full.
10. Chill: Place the filled tarts in the refrigerator for at least an hour to firm up.
11. Make the Mascarpone Cream: In a bowl, combine mascarpone, heavy cream, powdered sugar, and vanilla extract. Whip until soft peaks form.
12. Serve: Remove the tarts from the refrigerator. Top each tart with a generous dollop of mascarpone cream, and garnish with toasted sesame seeds and fresh berries if desired.

These simple yet effective steps will guide you through the process, ensuring each tart is beautifully crafted and ready to impress!