Take the pie crust out of the box. Leave it in the plastic and let it sit on your counter to soften up. An hour should do it.
You'll need a 9-inch fluted tart pan. Remove crust from package and lay it over the tart pan. Carefully ease the crust into the recesses of the tart pan. There will be about 1 inch of crust sticking over the top. Fold that over so the top of the crust lines up with the top of the tart pan. Poke holes in the crust with a fork to keep it from bulging up while baking. Look for cracks in the folds of the crust. If they are close to showing, try to push them back together with your fingers; otherwise your finished crust will have larger cracks when it expands as it bakes, and your filling could leak later.
Bake according to package directions for 400 degrees for 7 to 9 minutes. Cool.
Meanwhile, put your blueberries in the sauce pan with the sugar. Cook on medium high until the sugar melts and the mixture starts to bubble. Then add cornstarch one tablespoonful at a time. You might need to sift your cornstarch into the mixture. It's a real pain to get the white blobs back out if the cornstarch does not mix in well. Continue to cook mixture on medium. As it bubbles, it will get thicker with each addition of cornstarch. When it looks thicker, glossy and like pie filling, you are ready to let it cool down.
When cool, pour the tart filling in the crust. Spread it to the edges and sprinkle with slivered almonds in a 2-inch wide circle around the edge. Leave the middle plain for drama.