Beat together sugar and eggs, until blended. Heat milk and butter until butter is melted. Do not boil. Add all at once to egg mixture.
Combine flour and baking soda; gradually stir into mixture, stirring until well blended. Fold in blueberries,. Spread evenly into a greased 13x9 pan.
In a bowl, combine brown sugar and cinnamon. Cut in butter until crumbly, and sprinkle evenly over cake. Bake in 350F oven for 45 minutes, or until a toothpick inserted in center comes out dry.
BROWN SUGAR SAUCE;.
While cake is baking, make the sauce. In a saucepan combine brown sugar, flour and salt. Add boiling water and cook until slightly thickened. Remove from heat and stir in butter and vanilla. Serve warm over individual servings of blueberry cake. Garnish with a dollop of whipped cream or whipped topping.