Warm your tools: Rinse a medium heat-safe bowl with hot water, dry well, and set a flexible spatula and small saucepan nearby.
Heat the cream: Add the cream and salt to the saucepan and warm over medium-low heat until the edges show tiny bubbles and faint steam, 2–3 minutes. Do not boil. Remove from heat and stir in the vanilla.
Prep the chocolate: Place the white chocolate in the warmed bowl. Microwave for 10–15 seconds to take the chill off (do not melt); this helps it combine smoothly.
Emulsify in stages: Pour about one-third of the hot cream over the chocolate and let stand for 60 seconds. Stir from the center outward until a glossy core forms. Add the remaining cream in two additions, stirring each time until fully melted and uniform.
Smooth it out: For an ultra-silky finish, blend with an immersion blender for 10–15 seconds, keeping the head fully submerged to avoid introducing air.
Choose your finish: Use warm (95–100°F) as a pourable glaze; cool at room temperature 20–30 minutes for a spreadable filling; or for fudge-style squares, line an 8-inch pan with parchment, pour in the ganache, and refrigerate 60–90 minutes until firm before cutting.
Tip/troubleshooting: If the ganache looks oily or speckled, whisk in 1–2 teaspoons of warm cream until it comes back together.