- In a heavy medium sauce pan, add cornstarch and water, stir to combine. Cook over medium heat till cornstarch is dissolved.  
- Stir in the condensed milk and whisked egg yolks.  
- Cook until the mixture is thickened and starts to bubble.  
- Remove from the heat and add in the butter and vanilla. Stir till combined.  
- Allow to cool for about 30 minutes.  
- Fold in the 1/2 cup of toasted coconut.  
- Slice the bananas and dip them in the lemon juice.  
- Arrange bananas on the bottom of the pie crust. 
- Pour custard filling over the top of the bananas. Spread the top evenly.  
- Cover the pie and chill for 4 hours or overnight, till set.  
- Spread whipped cream over the top when ready to serve. 
- Sprinkle toasted coconut over the top, and arrange a few sliced bananas. 
- Serve.  
- Cover and refridgerate leftovers for 2-3 days.