Step 1: Preheat your oven to the temperature specified on your angel food cake mix box (usually around 350°F / 175°C). Do not grease your angel food cake pan.
Step 2: In a large mixing bowl, combine the angel food cake mix with 1/2 cup of water, 2 tablespoons of lemon juice (if using), and 1 teaspoon of vanilla extract.
Step 3: Mix on low speed for 30 seconds, then increase to medium speed and beat for 1 minute until the batter is smooth and well combined. Be careful not to overmix.
Step 4: In a separate small bowl, gently toss the fresh (or thawed and drained frozen) raspberries with 1/4 cup of sugar. This helps the raspberries hold their shape and sweetens them slightly.
Step 5: Gently fold the sugared raspberries into the cake batter using a spatula. Be careful not to crush the raspberries or deflate the batter too much.
Step 6: Pour the batter evenly into your ungreased 10-inch angel food tube pan. Gently level the top with a spatula.
Step 7: Bake according to package directions, typically 30-40 minutes, or until the top is golden brown and springs back when lightly touched.
Step 8: Immediately invert the cake pan onto its legs (or over a bottleneck) and allow it to cool completely, usually for at least 1-2 hours. This prevents the cake from collapsing.
Step 9: Once completely cool, run a thin knife around the edges of the pan and the center tube to loosen the cake. Invert onto a serving plate. Slice and serve as desired.