Step 1
Preheat the oven to 350 degrees F (175 degrees C).
Step 2
Blend together flour butter and sugar using an electric mixer in a medium-sized bowl. Press shortbread mixture into the bottom of an ungreased 9x9-inch baking pan.
Step 3
Bake in the preheated oven until firm and golden brown 15 to 20 minutes.
Step 4
Place cold water in a bowl to prepare raspberry filling. Sprinkle gelatin over water; stir. Let stand to soften about 1 minute.
Step 5
Puree raspberries using a food processor. Press berry puree through a fine mesh sieve into a medium saucepan; discard the seeds. Stir in gelatin mixture sugar and lemon juice.
Step 6
Bring mixture to a boil over medium-high heat. Reduce heat to medium and cook stirring frequently while skimming foam from sides of saucepan using a slotted spoon about 5 minutes. Reduce heat to medium-low. Cook stirring frequently until bright in color thickened and reduced by half 8 to 10 minutes.
Step 7
Pour raspberry filling over shortbread and let cool completely about 2 hours.
Step 8
Place cold water for lemon mousse in another bowl. Sprinkle gelatin over water; stir. Let stand to soften about 1 minute. Add boiling water; stir until gelatin is completely dissolved. Mixture will be clear.
Step 9
Combine heavy cream sugar lemon juice lemon extract and yellow food coloring in a large cold mixing bowl. Beat mixture at medium speed with an electric mixer until stiff peaks form. Pour in gelatin mixture and beat until well blended. Pour lemon mousse over firm raspberry filling and spread to cover. Allow to set completely about 4 hours before cutting into bars.