Yes, you're probably laughing at the thought of making toaster tarts when the boxed stuff is so convenient, but have you looked at what's in those? Here's a much healthier alternative, with natural ingredients and real fruit, that you can make today and bake them off quickly as you need them.
In a large bowl, combine flour, sugar and salt. Use a pastry cutter to cut in the cold butter for a coarse, crumbly pea-size mixture. Alternately, pulse in a food processor.
Sprinkle in the ice water and vinegar a tablespoon at a time while mixing. Bring mixture together by hand until it just comes together, do not over mix.
Form into two discs, seal well and chill for at least an hour.
In a medium pot over medium-high heat, bring the blueberries, sugar, lemon zest and juice to a boil, then reduce heat to low and simmer for 10 minutes until reduced.
In a separate small bowl, mix together cornstarch and cold water.
Add the cornstarch mixture and vanilla to the pot, return to a simmer and reduce for another minute. Set aside to cool.
Whisk all ingredients together in a small bowl.
Blueberry vanilla icing
In a medium pot over medium-high heat, bring the blueberries, sugar and milk to a boil. Reduce heat and simmer for 5 minutes until reduced, add vanilla. Pass through a fine mesh sieve for a smooth glaze. Allow to cool.
Pre-heat oven to 400°F with oven rack positioned in the centre. Line 2 baking sheets with parchment paper.
Remove dough from refrigerator 10 minutes prior to rolling.
Working with one disc of dough at a time, generously dust a clean surface with flour and roll it out into a 14" x 14" sheet that's ⅛” thick. Trim the edges and cut into 10 rectangles of the same size.
Brush the edges of one rectangle with egg wash then fill the centre with 1 tablespoon of cooled filling.
Lay another rectangle over the jam-filled pastry. Press around edges with the tines of a fork to seal. Poke holes on top for steam to escape.
Repeat process for other remaining pastry.
Brush top and edges with egg wash, sprinkle with coarse sugar and bake for 15 minutes until golden brown.
Drizzle icing over baked tarts.