For the Cookies: 

1. Sift together the flour, baking powder, and salt in a medium bowl. 
2. Cream together the sugar and butter with a stand or handheld mixer until pale in color and light and fluffy. Beat in the eggs and the lemon juice. 
3. Add the dry ingredients to the butter-sugar mixture slowly, continuing to beat, just until combined.  
4. Scoop the dough into balls with a small ice cream scoop, and place on a tray or baking sheet. Refrigerate the balls of dough for at least 1 hour. 
5. Preheat the oven to 325 degrees. Line a pair of baking sheets with parchment paper. 
6. Arrange about 9 tennis biscuits, side-by-side on each baking sheet. Roll cookie dough balls in the turbinado sugar and top each tennis biscuit with a ball.  
7. Bake for 15 to 16 minutes, rotating the baking sheets halfway through the baking time. Then let cookies cool to room temperature. 

For the Peppermint Crisp Filling:

1. Whip the cream in a large mixing bowl until soft peaks form. Add the dulce de leche and beat it in. Fold in the candy bar pieces. 
2. Spoon the filling into a piping bag fitted with a round tip. Pipe the filling in a circular pattern around the top of each cookie. Sprinkle with additional chopped candy bar pieces over the top of each and serve.