In medium saucepan heat half-and-half and vanilla bean over medium heat until steaming (140 degrees F to 145 degrees F), about 3 minutes (too hot to insert a finger for more than a moment). Remove from heat; cover. Steep for 15 minutes.
Position rack in lower third of oven. Preheat oven to 350 degrees F. In small bowl combine brown sugar and 1/4 tsp. of the salt, pinching and mashing to eliminate lumps. Spoon mixture into 9-inch deep pie plate. Pack into firm, even layer.
Remove bean from half-and-half (let cool if hot to handle); cut bean lengthwise. With point of small knife, scrape seeds from bean and add to half-and-half. Briefly reheat mixture for 1 to 2 minutes, just to steaming.
In large bowl whisk eggs, granulated sugar, and remaining 1/4 tsp. salt. Gradually whisk in warm half-and-half until well-combined.
Slowly pour egg mixture in pie plate over brown sugar. Some sugar may float up but will settle to bottom eventually.
Place pie plate in deep roasting pan. Place pan in oven. Pour boiling water in roasting pan to halfway up sides of pie plate. Bake 35 to 40 minutes or until a knife inserted in center comes out clean.
Carefully remove pie plate from roasting pan. Cool on wire rack 30 minutes. Cover and refrigerate at least 6 hours or overnight. To serve, gently run a thin metal spatula or knife around edge of flan. Invert onto serving plate. Makes 8 servings.