Preheat your oven to 350°F (175°C). Grease a 9x13-inch baking dish.
In a large bowl, combine the sliced strawberries, blueberries, and raspberries. Add ½ cup of sugar, lemon juice, cornstarch, and vanilla extract. Toss to coat the berries evenly. Pour the mixture into the prepared baking dish.
In another bowl, whisk together the flour, baking powder, salt, and the remaining ½ cup of sugar. Add in the melted butter and milk. Stir until just combined; be careful not to overmix.
Pour the batter over the berry mixture in the baking dish. Spread it out gently to cover as much of the berries as possible. Don’t worry if some of the berries poke through.
In a small bowl, mix together the ground cinnamon and 1 tablespoon of sugar. Sprinkle this mixture over the cobbler batter.
Bake in the preheated oven for about 45-50 minutes, or until the top is golden brown and a toothpick inserted into the batter comes out clean.
Allow the cobbler to cool for about 10-15 minutes. Serve warm with a scoop of vanilla ice cream or whipped cream if desired.
Notes
Serve warm with vanilla ice cream or whipped cream for an extra treat.