Make meringues: Preheat oven to 200°. Separate 6 eggs and put whites into the metal bowl of a stand mixer; set yolks aside. Add 3/4 cup granulated sugar to whites. Set bowl over a pan of simmering water and whisk until slightly warm, about 1 1/2 minutes.
Using whisk attachment, beat whites with mixer on high speed until they hold a straight peak when beater is lifted, 1 1/2 to 2 minutes. Sift powdered sugar and 1/4 cup granulated sugar into another bowl. Gradually add sifted sugars to whites (about 1/4 cup every 30 seconds), beating on high speed once sugar is incorporated, until mixture holds a stiff, straight peak when beater is lifted, 5 to 8 minutes; check often and do not overbeat.
Line 2 large baking sheets with parchment paper and glue down corners of paper with dabs of meringue. Spoon 6 equal mounds of meringue (1/2 to 2/3 cup each) onto each sheet, spacing evenly. With back of a soup spoon, spread each mound into a circle about 3 1/2 in. wide with a 2-in.-wide hollow in the center.
Bake meringues until firm, about 1 1/2 hours. Turn off oven and leave meringues in oven to firm overnight.
Meanwhile, make lemon curd: Finely shred zest from 2 lemons. Squeeze juice from enough lemons to make 1 cup. In a metal bowl, whisk zest, juice, remaining 1 cup granulated sugar, the egg yolks, and remaining whole egg to blend. Add butter. Stir mixture over a pan of simmering water until it thickly coats a metal spoon, 10 to 15 minutes. Let cool, whisking often. Cover with plastic wrap directly touching curd and chill until cold, at least 2 hours.
Loosen meringues from parchment, put on plates, and spoon about 1/4 cup lemon curd into each. Scatter some berries onto meringues and serve the rest from a bowl.
Make ahead: Up to 4 days ahead, prepare curd and meringues; fill up to 1 hour ahead.
Note: Nutritional analysis is per serving.