Preheat oven to 350 degrees F. Butter a 10-inch glass pie plate.
Wash, stem, and dry blackberries; set aside.
Place butter in a microwave-safe dish and melt; set aside.
In a large mixing bowl, place 1 cup sugar, Bisquick mix, and cinnamon. Whisk in the milk and then add the melted butter, mixing thoroughly.
Pour the batter into the prepared pie plate. Distribute the blackberries over the top of the batter, as evenly as possible. Sprinkle the remaining 1/4 cup sugar over the top of the blackberries.
Bake, uncovered, 50 to 60 or until crust is bubbly and golden in color. NOTE: I checked after 45 minutes and it was almost done. I gave it another 5 minutes.
Remove from oven and let cool on a wire rack for at least 10 minutes before serving. Serve either warm or room temperature. To serve, top with vanilla ice cream.
Makes 4 servings.
Blackberry Cinnamon Cobbler Recipe: https://whatscookingamerica.net/karencalanchini/cinnamonblackberrycobbler.htm