Grease your baking dish with butter. Make sure it is a thin layer and not a thick coating.
Place your blackberries in the greased dish.
Now take a bowl and combine sugar, cornstarch, water, and lemon juice and mix until you get a smooth textured mixture. (don’t make the mixture too thin/runny). Pour over the blackberries.
Now take another bowl and combine oats, flour, brown sugar, and cinnamon and mix together.
Now add the butter in the dry mixture you have created and mix it till it is entirely crumbly and not in separate lumps. Put in the berries too.
Now preheat the oven to 375 degrees Fahrenheit.
Put in the dry mixture over the wet mixture and toss the dish into the oven and bake.
Bake it for 30 to 40 minutes or until the top is golden-brown, and fruit is in bubbles (boiling).
Once the crisp is ready, let it cool for about 30 minutes before serving.
Serve your mouth watering crisp with any ice cream (tastes best with vanilla ice cream) or highly sweetened whipped cream or icing.