01 - Preheat the oven to 350°F. Grease a 9x13-inch baking dish or similar deep casserole.
02 - In a large bowl, combine peaches, sugar, Southern Comfort, lemon juice, vanilla, cinnamon, and salt. Toss to coat and set aside to macerate for 10 minutes.
03 - In another bowl, whisk together flour, sugar, baking powder, and salt. In a separate bowl, beat together melted butter, eggs, milk, and vanilla. Pour wet ingredients into dry and stir until just combined.
04 - Pour the boozy peach mixture into the prepared baking dish, spreading evenly. Dollop the cake batter over the peaches in large spoonfuls; it's fine if some fruit peeks through.
05 - In a small bowl, combine oats, brown sugar, flour, cinnamon, and salt. Rub in the cold butter with your fingers until the mixture forms coarse crumbs. Scatter evenly over the cake batter.
06 - Bake for 40–45 minutes, until the top is golden, the edges are bubbling, and a toothpick inserted into the cake comes out clean.
07 - Let cool for at least 20 minutes. Serve warm, scooping "messy" portions into bowls. Top with ice cream or whipped cream if desired.