Before you do anything else, gather every ingredient and position everything you'll need within arm's reach. Preheat your oven to 375°F. Line a 9-by-13-inch baking dish with parchment paper, or simply grease it well with butter—I prefer parchment because it makes cleanup infinitely easier and means you can lift the finished crisp out cleanly. Cut your frozen butter into small cubes and place it directly in the freezer while you prepare the fruit. This matters more than you might think. Cold butter creates steam pockets; warm butter creates a dense, greasy topping. If your kitchen is particularly warm, keep the butter cubes in the freezer until the exact moment you need them.

Fresh peaches are wonderful, but they need respect. To peel them, bring a large pot of water to boil, then carefully lower your peaches into the boiling water for exactly 30 seconds. Remove them with a slotted spoon and immediately submerge them in ice water. The skin should slip off easily. Slice each peach into ½-inch thick pieces—this thickness is specific because it allows the fruit to soften completely during baking while maintaining distinct pieces rather than becoming applesauce. Place the sliced peaches and blackberries in a large mixing bowl. If your blackberries are frozen, that's perfectly fine—don't thaw them first. The frozen berries will help keep the filling cool and prevent over-thickening before it reaches the oven.

In a small bowl, whisk together your cornstarch, coconut sugar, orange zest, and salt. This is where many people make a critical mistake—they try to mix cornstarch directly into the wet fruit and create lumps. Instead, combine the cornstarch with the sugar first. The sugar granules separate the cornstarch particles, preventing them from clumping when liquid is introduced. Add the orange juice to this mixture and stir until you have a smooth slurry with no visible cornstarch lumps. This slurry will distribute evenly through the fruit.

Pour the cornstarch mixture over your fruit and fold gently with a rubber spatula. Don't stir vigorously—aggressive stirring breaks down the fruit and creates mush. Instead, use a folding motion: push your spatula to the bottom of the bowl, fold the bottom over the top, rotate the bowl slightly, and repeat until the cornstarch mixture is evenly distributed. You should see flecks of orange zest throughout and every piece of fruit should be lightly coated. Transfer this mixture to your prepared baking dish, spreading it in an even layer. If you have time, let this sit for 15-20 minutes while you prepare the topping. This resting period allows the fruit to begin releasing its moisture naturally, which means less liquid will seep from the sides of the baking dish during baking.

This step requires a food processor and your full attention. Add the frozen butter cubes, brown sugar, ¾ cup of the oats, and flour to your food processor. Pulse—don't run continuously—until the mixture resembles coarse sand with some pea-sized pieces of butter still visible. This should take about 8-12 pulses. This texture is crucial. If you process too long, the butter warms up and the topping becomes dense instead of crispy. Transfer this mixture to a bowl and add the remaining ¼ cup of oats. Use your hands to gently toss until the raw oats are distributed throughout. You want some portions that are more flour-based and crispy and some portions that are more oat-forward and chewy. This variation in texture is what makes a really exceptional crisp.

Scatter the oat topping over your fruit filling, breaking up any large clumps as you go. Don't press it down—you want it to be loose and airy so steam can circulate underneath. The fruit will expand as it bakes and gently push against the topping, creating its own leverage. Place the baking dish in your preheated 375°F oven and bake for 50-60 minutes, until the topping is deep golden brown and you can see fruit juice just beginning to bubble around the edges of the pan. A few dark bits on top are perfect—this indicates proper caramelization. If your topping seems to be browning too quickly after 30 minutes, lower the oven temperature to 350°F for the remaining time. When the crisp comes out of the oven, let it rest for at least 10 minutes before serving. This resting period allows the filling to set slightly so it won't run all over your plate. Even better, let it cool for 30 minutes—it will be warm and wonderful, and the flavors will have time to integrate.

Scoop the crisp into bowls while it's still warm and top with a generous scoop of vanilla ice cream. That cold ice cream melting into warm, spiced fruit and crispy oats is not just delicious—it's the moment people relax and actually enjoy your gathering.