Beat the egg whites with a mixer until they reach stiff peaks.
Gradually add the sugar, lemon juice and cornstarch.
Transfer the meringue mixture into a piping bag and line a baking tray with baking paper.
Pipe small circles of meringue onto the tray, forming low edges to create nests. Bake at 212 °F, for 2 hours.
Prepare the cream: beat the heavy cream with the powdered sugar, then once it is smooth, add the mascarpone and beat again.
When the meringue bases are ready, let them cool completely. Put the prepared cream in a piping bag, use a metal tip and fill the meringue nests with cream.
Decorate with berries and, if you like, a few small mint leaves. Dust lightly with powdered sugar.