Spray an 8x8 inch square pan with cooking spray and then place a double layer of cling film into the pan, with overhang to make it easy to pull the fudge out. Spray the cling film with cooking spray too.
Place crushed cookies into a medium sized bowl and then pour the melted butter into the bowl. Mix until all of the cookie crumbs are coated in butter.
Tip the cookie crumbs into your prepare pan and press firmly into an even layer. I use the bottom of a measuring cup do this. Place in the fridge for 30-45 minutes.
Once chilled, place the condensed milk and white chocolate into a medium sized saucepan and place over a low heat, stirring frequently until all of the chocolate is melted and the mixture is smooth.
Add in the lemon extract, butter and yellow food colouring (if using) and stir until the butter is melted. Leave to cool in the pan for 10 minutes.
Tip in the crushed meringue pieces and fold in until all the meringue pieces are covered in the fudge mixture.
Tip the fudge mixture on top of your shortbread base and smooth into an even layer with the back of a spoon/spatula. Sprinkle the top with extra meringue pieces, if desired and leave to cool for 1 hour.
After the fudge has cooled, place in the fridge until set, around 2 hours. Once set, wiggle the cling film loose and lift out from the pan. Peel away the cling film from the fudge and place on a cutting board.
Either cut into 24 squares, or cut into 4 strips and then cut diagonally across to create a piece of fudge that look like a slice of pie. You will end up with 48 pieces of fudge this way.
Lemon Meringue Pie Fudge will keep in an airtight container, in the fridge, for 4 days.