Preheat your oven to 350°F (175°C). Lightly grease an 8 or 9-inch cast-iron skillet or round baking pan.
In a small bowl, toss your chopped stone fruit with the lemon juice and set aside.
In a medium bowl, whisk together the flour, baking powder, baking soda, and salt.
Using an electric mixer or hand whisk, beat the softened butter and granulated sugar together until light and fluffy.
Add the eggs one at a time, followed by the vanilla extract, beating until smooth.
Alternate adding the dry flour mixture and the ricotta cheese to the wet ingredients. Mix on low speed just until combined to keep the texture light.
Gently fold in the chopped stone fruit. Spread the thick batter evenly into your prepared skillet or pan.
In a separate small bowl, combine the oats, flour, brown sugar, and almonds. Use your fingertips to rub the cold cubed butter into the mixture until it forms coarse, gravel-like crumbs.
Sprinkle this mixture evenly over the top of the cake batter.
Bake for 50 to 55 minutes. The center should be set, and a toothpick inserted into the cake part should come out clean.
Let the cake cool in the pan for at least 10–15 minutes before slicing. It is delicious served warm on its own or with a scoop of vanilla ice cream.