Preheat oven to 350ºF (180ºC). Toast nuts on a baking tray until golden brown, about 10 min; let cool. Reserve 1/4 cup (60 ml) for garnish. In a food processor, finely grind remaining nuts, and set aside.
Reduce oven to 250ºF (120ºC) and line two baking trays with parchment paper; lightly grease with butter or cooking spray and set aside. Using a hand mixer, whisk egg whites and cream of tartar until frothy. Gradually add sugar while whisking at low speed; slowly increase speed to high, whisking until glossy with stiff peaks.
Gently fold ground nuts into egg whites until just combined. Using a large piping bag, pipe meringue onto baking trays in two 9-inch (23 cm) circles, piping in concentric circles from outside towards the centre. Smooth tops with a spatula and bake for 90 min. Turn pans, bake another 30 min, until meringues are dry throughout. Turn off oven and let meringues sit for 30 min. Remove from oven, transfer to a rack and let cool completely.
To make filling, whisk cream, icing sugar, coffee and vanilla in a large bowl with a hand mixer to stiff peaks. To assemble, place a dollop of cream on a platter and set a meringue on top. Cover with half the cream, blueberries, reserved nuts and caramel sauce, repeat with remaining ingredients. Cover and refrigerate for 20 minutes; slice and serve.
If you don’t have a piping bag, you can use a large sealable plastic freezer bag instead. Fill it with the meringue and cut off one of the corners, it works just like a piping bag.