If desired, peel peaches. Thinly slice. If using canned peaches, drain well. Toss peaches with brown sugar, granulated sugar, and cornstarch. Set aside.
Combine Bisquick mix, milk, cinnamon, and vanilla in a medium mixing bowl. Pour into an ungreased 9x9" baking dish. Melt butter and stir into Bisquick mixture until just combined.
Layer peaches on top of Bisquick mixture (it will rise around the peaches as it bakes).
Bake for 50-60 minutes or until a toothpick inserted into the center comes out clean. Serve warm with vanilla ice cream.
Notes
If using fresh peaches, firm hold up better when baked.If using canned peaches, drain well. I like to place them on a paper towel to help remove any excess moisture.