In bowl of electric mixer and using whisk attachment, beat egg whites on medium-low speed until foamy. Beat in cream of tartar until soft peaks form. Beat in 1/2 cup (125 mL) of sugar, a little at a time, until stiff peaks form.
    
Transfer meringue to pastry bag fitted with 1/2-inch (1 cm) plain or star tip (or use 2 spoons). Pipe 2-inch (5 cm) rounds in rows on parchment paper-lined baking sheets to make 20 rounds.
    
Bake in 250°F (120°C) oven for 1 hour, rotating sheets from top to bottom and front to back halfway through or until pale ivory and firm enough to lift from pan without sticking. (Test by removing 1 meringue and letting it cool for a few minutes. It should be crisp and dry when broken in half.) Turn off oven; open door and leave meringues in oven to dry for a few hours.

Place 2-1/2 cups (625 mL) of the strawberries in food processor along with 1 tbsp (15 mL) of the sugar and lemon juice; process until puréed. Set aside.

Slice remaining strawberries into bite-size pieces; place in bowl. Sprinkle remaining sugar over top; stir to combine.

Break about 12 meringue cookies into bite-size pieces; set aside.

In large bowl, with electric mixer, on medium-high speed, whip cream until soft peaks form. With rubber spatula, gently fold in 1 cup (250 mL) of the strawberry purée. Just before serving, fold in 1 cup (250 mL) of the sliced strawberries and crumbled meringues. Fill 8 parfait or long-stemmed glasses half full of whipped cream mixture. Top with remaining sliced berries. Place 1 whole meringue cookie on top. Top with remaining whipped cream mixture. Drizzle remaining strawberry purée over top.

Tip: Before placing cookies on cookie sheet, place a little meringue on underside of each corner of parchment paper to prevent paper from sliding.