Heat half-and-half or light cream in a small heavy saucepan over medium-low heat just until bubbly. Combine slightly beaten egg yolks, 1/3 cup sugar, vanilla, and salt in a medium mixing bowl. Beat with a wire whisk or rotary beater just until combined. Slowly whisk or stir the hot cream into the egg mixture.
Place four ungreased 4-inch quiche dishes or oval or round tart pans without removable bottoms into a 13x9x2-inch baking pan. Set the pan on an oven rack in the preheated oven. Pour custard mixture evenly into the dishes. Pour very hot water into the baking pan around the dishes until water is halfway up the sides of the baking pan.
Bake for 18 to 24 minutes or until a knife inserted near the center of each dish comes out clean. Remove dishes from pan; let cool about 30 minutes. Cover, chill for 1 hour or up to 8 hours. Before serving, let the custards stand at room temperature for 20 minutes.
Place 1/3 cup sugar in a heavy 10-inch skillet. Heat skillet over medium-high heat until sugar begins to melt, shaking skillet occasionally to heat sugar evenly. Do not stir. Once sugar starts to melt, reduce heat to low; cook until sugar is completely melted and golden (3 to 5 minutes more), stirring as needed.
Spoon melted sugar quickly over custards in a lacy pattern or in a solid piece. If melted sugar starts to harden in pan, return to heat, stirring until it melts. If it starts to form clumps, carefully stir in 1 to 2 teaspoons water. If desired, garnish custards with edible flower petals. Serve immediately. Makes 4 servings.