To make the praline sauce, heat ½ cup of butter in a large saucepan until melted. Use a large saucepan, as the mixture will foam. Add pecans to melted butter and mix well. Bring to a boil. Boil until the pecans begin to change color. Add the remaining butter and mix well, then remove from heat. In a second saucepan, combine the brown sugar, heavy whipping cream and cinnamon, and mix well. Cook over low heat until the mixture has blended, stirring constantly. Increase the heat, and continue stirring. Cook until the temperature reaches 230º (use a candy thermometer). Stir in the pecan mixture. Add the sour cream and vanilla, and mix well. Remove from heat.