Using an electric mixer, beat 1 stick butter and 1/4 cup sugar until fluffy, about 2 minutes. Stir in the egg and yolks one at a time, then beat for 1 minute. (The mixture may look curdled.) Add 1/2 cup chopped pineapple and the lemon juice and mix until smooth.
Transfer the mixture to a medium, heavy saucepan and cook over medium heat, whisking, until thick enough to coat a spatula, 6 to 7 minutes. Remove from the heat and let cool to room temperature, whisking occasionally.
Transfer the pineapple curd to a medium bowl and press plastic wrap directly on the surface. Refrigerate the curd for about 1 hour.
In a small bowl, whip the cream until stiff. Fold the whipped cream into the chilled pineapple curd. Refrigerate the pineapple mousse for 3 hours or overnight.
Meanwhile, preheat the oven to 350 degrees . Line 2 baking sheets with parchment paper. Place the remaining 1/2 cup pineapple in a strainer to drain, pressing with the back of a spoon to remove any excess juice. Transfer the pineapple to a medium bowl; add the remaining 1 cup sugar, the flour and the melted butter and stir until smooth. Refrigerate the batter for about 10 minutes.
Drop a heaping tablespoon of batter on a prepared baking sheet. Spread the mixture into a round about 2 inches wide. Repeat with the remaining batter to make 4 rounds. Bake until golden and bubbly, about 10 minutes. Let the wafers sit until cooled slightly but still pliable, 1 to 2 minutes. Using a metal spatula, invert the wafers onto upside-down cups. (If the wafers become too stiff to bend, return them to the oven for a minute or so to soften.) Let cool completely.
Spoon the chilled mousse into the cookie cups and top with chopped pineapple.