2. Cut your nectarines into approximately 1" pieces, and your strawberries into halves or quarters.
3. In a large bowl, combine the cut fruit with the sugar, lemon juice and cornstarch. If your nectarines are super juicy, you may want to add an extra teaspoon of cornstarch.
4. In a medium bowl, combine the flour, brown sugar, oats, cinnamon and salt.
5. Cut the butter into small cubes and using your fingertips, combine it into the dry ingredients with your fingertips until the mixture resembles coarse meal. Stir in the walnuts or pecans, if using. If you are not baking immediately, place topping back into the fridge to keep the butter cool until you're ready to use it.
6. Spread your fruit mixture into a glass or ceramic 13x9 pan* and evenly sprinkle your topping over.
7. Bake in the middle of the preheated oven for 40-50 minutes or until the topping is golden and fruit is bubbling.
8. Let the crisp cool for 30 minutes or more so the juices can thicken as they cool.
9. Serve the crisp warm or at room temperature with vanilla ice (or vegan "nice") cream.
Notes
*You can also use four small pie plates, as shown in the photos.