Place 100 grams chopped white chocolate in a heatproof bowl.
Heat heavy cream in a small pan just until it begins to sizzle at the edges. Do not boil.
Pour the warm cream over the chocolate. Let sit 5 minutes without stirring.
Whisk until smooth ganache forms. Add vanilla if using. If any chocolate remains unmelted, microwave the bowl in 10-second bursts, whisking between each, until smooth.
Press plastic wrap directly onto the surface of the ganache. Refrigerate 2 to 3 hours until firm.
Line a tray with parchment. Use a mini cookie scoop to drop small mounds of ganache onto the tray. Do not shape yet. Refrigerate 30 minutes.
Working quickly, push each mound from both sides to form a rough ball and roll once between palms. Return to the refrigerator 10 minutes.
Melt white chocolate for coating in a heatproof bowl over simmering water or in the microwave in 15-second bursts, stirring until smooth. Cool 1 to 2 minutes until slightly thickened but still fluid.
Dip each chilled truffle in the white chocolate, turning with a fork so it is fully coated. Tap off excess, set on parchment, and refrigerate 20 to 30 minutes until firm. Keep chilled while you prepare the besan mixture.