6 large egg yolks
1 cup sugar
4 lemons, zested and juiced
1/2 cup (1 stick) unsalted butter, cut in chunks
1 pint fresh strawberries, stemmed and halved lengthwise
1 pint fresh blueberries
1 pint fresh blackberries
2 cups sweetened whipped cream
1 prepared lemon pound cake, sliced
1/4 cup Limoncello or Grand Marnier liqueur (optional)
Fresh mint leaves, for garnish