Preheat oven to 350°.
Line a 15 1/2 x 10 1/2-inch jelly roll pan with parchment paper. Coat parchment paper with cooking spray; dust with cocoa.
Combine cake mix, water, baby food, and eggs in a large bowl; beat with a mixer at medium speed 2 minutes. Spread cake batter into prepared pan.
Bake at 350° for 23 minutes or until cake springs back when touched lightly in center. Cool cake in pan 10 minutes. Loosen cake from sides of pan, and invert onto a wire rack. Remove parchment paper. Cool completely. Cut cake crosswise into 3 equal pieces to create 3 rectangular cake layers.
Combine preserves and liqueur in a small bowl; stir until smooth.
Place 1 cake layer on a cake platter; spread with half of raspberry mixture, leaving a 1/2-inch border. Repeat procedure with second cake layer and raspberry mixture. Top with third cake layer. Cover and chill 8 hours. Sift powdered sugar evenly over cake before serving.
To slice the finished cake into triangles, slice cake lengthwise down the center. Cut widthwise into 4 equal squares and cut each square diagonally. Garnish with raspberries, if desired.