Preheat oven to 350°F and line with parchment paper or grease a 9x13-inch baking pan.
Mix together the cake mix, melted butter, and egg until combined.
Press the mixture evenly into the bottom of the prepared pan
In another bowl, whisk together the sweetened condensed milk and lemon juice until smooth.
Gently fold in the raspberries.
Pour the raspberry mixture evenly over the crust.
Bake for 45–55 minutes, until the edges are lightly golden and the center is set.
Cool completely, then refrigerate for at least 1 hour before slicing into bars.