Step 1: Prepare the Gelatin - In a small mixing bowl, sprinkle the unflavored gelatin over the skim milk. Let it sit for about 5-10 minutes until it blooms and thickens slightly.
Step 2: Heat the Cream Mixture - In a medium saucepan, combine the heavy whipping cream, sugar, and vanilla extract. Place the saucepan over medium heat, stirring occasionally until the mixture is hot but not boiling. Remove it from the heat.
Step 3: Combine Gelatin and Cream - Once the cream mixture is hot, add the bloomed gelatin mixture to the saucepan. Whisk vigorously until the gelatin is completely dissolved and the mixture is smooth.
Step 4: Chill the Panna Cotta - Pour the panna cotta mixture into your prepared serving glasses or ramekins. Allow them to cool to room temperature, then cover with plastic wrap and refrigerate for at least 4 hours or until set.
Step 5: Make the Raspberry Sauce - In a small saucepan, combine the fresh raspberries, sugar, and lemon juice. Cook over medium heat until the raspberries break down and the mixture thickens, about 5-7 minutes. Strain through a fine mesh sieve to remove the seeds, if desired.
Step 6: Serve - Once the panna cotta is set, remove it from the refrigerator. Top with the raspberry sauce and fresh berries just before serving for a stunning presentation.