In small pan, over medium heat, mix cream and lemon extract. Chop white chocolate baking bars and add to pan. Add salt and butter to pan, stirring constantly. When mixture beings to simmer, whisk in powdered sugar and lemon juice. Stir mixture over heat til sugar is dissolved, 2 to 3 minutes. Remove from heat and put in glass bowl to cool. Cover and chill in refrigerator for 4 hours.
Put sugar in small bowl. Remove truffle base from refrigerator. using a small cookie scoop or small spoon, form balls. Roll the balls in sugar til well coated to form truffles. Store in refrigerator before serving.