To make the custard: Add the cream, lavender, vanilla, and salt to a heavy-bottomed 2-quart saucepan set over moderate heat. Stir occasionally with a wooden spoon or whisk. When the mixture begins to simmer (tiny bubbles will form around the edge of the pan), remove the pan from the heat and let the mixture sit at room temperature for at least 1 hour to allow the flavor of the lavender to steep into the cream. Or, to extract the maximum flavor, cool the mixture to room temperature, cover, and refrigerate overnight.
Preheat the oven to 325°F with the rack in the center position. Reheat the infused cream to a bare simmer, stirring once or twice. In a large mixing bowl, whisk together the egg yolks and sugar until light yellow and slightly thickened. Pour in the hot cream, whisking to mix completely. Strain the custard through a fine sieve into a large measuring cup or spouted pitcher, and skim off any bubbles.
Fill six 8-ounce ramekins or brûlée dishes almost to the top with the custard, and place them in a shallow roasting pan or heavy-duty rimmed baking sheet, so that the edges are not touching. Add hot water to come halfway up the sides of the ramekins. Cover the pan loosely with foil and bake for 35 to 45 minutes (depending on the density of the ramekin or dish), or until the custards are set up and the tip of a sharp knife inserted in the center comes out clean.
Transfer the ramekins to a wire rack to cool to room temperature, then refrigerate, uncovered, to cool completely.
To make the topping: At least 30 minutes before serving, sprinkle the top of each custard with a generous amount of sugar. Using a kitchen blowtorch (available from a hardware or kitchenware store), melt the sugar by moving the flame slowly back and forth over the surface until the sugar bubbles and has liquefied. Return the brûlée to the refrigerator to allow the topping to harden (about 15 minutes).