Blueberry Pie

3 1/2 - 4 c. blueberries - frozen ones are the best to use; thaw first
2/3 - 1 1/2 c. sugar - to taste
3 Tbsp + 1 tsp. cornstarch
1 Tbsp. lemon juice
2 Tbsp. butter

Place fruit, sugar (start with less), cornstarch in saucepan and mix until smooth.  Cook over medium heatm stirring occasionally (whisk) until mixture is thick and clear - about 7-10 minutes.  Remove from heat.  Stir in lemon juice.  Add butter and let butter melt on top of mixture before incorporating.  Stir well and taste.  Add more sugar if necessary but make sure to incorporate well.  Pour into a baked pie shell and chill until firm.  Serve with whipped cream if desired.