Preheat your oven to 375°F (190°C). This ensures that the cobbler bakes evenly.

In a large mixing bowl, combine the chopped rhubarb, sugar, flour, vanilla extract, cinnamon, and lemon juice. Toss until the rhubarb is evenly coated. This mixture will create a sweet and tangy filling.

Transfer the rhubarb mixture to a greased 9x13 inch baking dish, spreading it out evenly.

In a separate mixing bowl, whisk together the flour, baking powder, salt, and sugar. This helps to aerate the dry ingredients.

Add the cold, cubed butter to the flour mixture. Using a pastry cutter or your fingers, work the butter into the flour until the mixture resembles coarse crumbs. This step is crucial for a flaky biscuit topping.

Pour in the milk and vanilla extract, stirring gently until just combined. Be careful not to overmix, as this can make the biscuits tough.

Drop spoonfuls of the biscuit dough over the rhubarb filling, leaving some gaps for the filling to bubble up. This creates a rustic look and allows the filling to peek through.

Place the baking dish in the preheated oven and bake for 35-40 minutes, or until the biscuit topping is golden brown and the filling is bubbling. The bubbling indicates that the rhubarb is cooked and the flavors are melded.

Once baked, remove the cobbler from the oven and let it cool for about 10 minutes before serving. This allows the filling to set slightly.

Serve warm, optionally with a scoop of vanilla ice cream or whipped cream for added indulgence.