Preheat the oven to 350℉. Arrange the frozen tart shells on a baking sheet. Bake the empty tart shells for 15 minutes.

In a mixing bowl, whisk together the sugar and flour until combined. Add the sweetened condensed milk, eggs, sour cream, and vanilla and mix until fully incorporated. Lastly, add the lemon juice and whisk until smooth.

Distribute the filling evenly between all 20 pre-baked tart shells. Return the pan to the oven and bake for 15-20 minutes or until the lemon filling is set and no longer jiggly when you wiggle the pan. Remove from the oven and let cool to room temperature before transferring to the refrigerator to chill for at least 1 hour before serving.

Once the tarts have chilled or right before serving, top each tart with a few fresh raspberries. Add a dusting of powdered sugar right before serving for a pretty garnish, if desired. Enjoy!