Preheat your oven to 375°F. While it heats, combine the oats, almond meal, brown sugar, cinnamon, and salt in a bowl and mix until evenly distributed. Cut 5 tablespoons of cold butter into small cubes and add them to the dry mixture, then use your fingertips to work the butter into the oats until the mixture resembles coarse breadcrumbs with some pea-sized butter pieces remaining. This texture is crucial for creating a crispy, buttery topping. Set aside while you prepare the fruit.

Melt 3 tablespoons butter in your cast iron skillet over medium heat. Add the rhubarb, strawberries, and sugar, stirring gently to coat the fruit. Let it cook for about 5 minutes, stirring occasionally, until the fruit begins to soften and release its juices. In a small bowl, whisk together the orange juice, cornstarch, and vanilla until completely smooth with no lumps—the cornstarch is what will thicken the fruit juices and give the crisp a nice jammy consistency.

Pour the orange juice mixture from Step 2 over the cooked fruit in the skillet, then stir gently for about 1 minute to combine everything evenly. The cornstarch will begin to thicken the juices slightly and coat the fruit. Sprinkle the nutmeg over the top and give it one final stir. I like to use fresh orange juice here because it adds a bright acidity that balances the sweetness of the rhubarb and strawberries beautifully.

Spread the crisp topping from Step 1 evenly over the fruit filling in the skillet, breaking up any large clumps gently with your fingers so it's distributed fairly uniformly. Don't compress it—you want it to stay light and airy so it can bake up crispy. Place the skillet in the preheated 375°F oven and bake for 30 minutes, until the topping is golden brown and the fruit filling is bubbling around the edges of the skillet.

Remove the skillet from the oven carefully and let it cool for about 10 minutes at room temperature. This resting time allows the filling to set slightly so it won't be watery when you scoop it out. Serve warm, directly from the skillet, with vanilla ice cream or whipped cream if desired.