Place white chocolate in pyrex measuring cup or glass bowl. Microwave for 2 minutes on 50% power. Remove from microwave and stir. If there are still lumps, microwave in 30 second intervals until melted. Be sure to stir each time. Set aside. At most you should need 3 minutes at 50% power.

Pour milk into heavy bottomed saucepan (if using vanilla bean, slit down center, scrape out seeds and add seeds and bean to milk). Place over high heat and scald. A skin will form on the surface and you can remove it or leave it in since the custard will be strained at the end.

Whisk yolks and sugar in small bowl until thick and light yellow. Whisk in 2-4 tablespoons hot milk. Stir yolks back into remaining milk and whisk.

Over medium-low heat stir until thick enough to coat the back of a spoon. Using an instant read or candy thermometer, do not let the temperature go over 180F or the eggs will curdle.

Immediately strain into bowl (stainless steel is best because it will cool faster once the bowl is set over ice).

Stir in the Kahlúa and vanilla (if using extract). Whisk in the melted white chocolate. Cool the mixture (this can be done quickly by placing bowl over an ice bath). Alternatively, place in refrigerator at least 2 hours or overnight, until cold. When cold enough (40F or less) pour into ice cream maker. Process according to manufacturers instructions. Enjoy!