Preheat your oven to 325°F (160°C). This ensures your cheesecakes will bake evenly.
In a mixing bowl, combine the graham cracker crumbs, granulated sugar, kosher salt, and melted unsalted butter. Stir until the mixture resembles wet sand.
Take a tablespoon of the crumb mixture and press it firmly into the bottom of each muffin cup. Use the back of a spoon or your fingers to create an even layer. Bake the crusts in the preheated oven for about 8 minutes, or until lightly golden. Remove and let them cool slightly.
In a large mixing bowl, beat the softened cream cheese using an electric mixer until smooth and creamy. Add in the ricotta cheese, granulated sugar, and vanilla extract. Mix until well combined.
Add the eggs and egg yolk one at a time, mixing well after each addition. Make sure to scrape down the sides of the bowl to ensure everything is evenly incorporated.
Finally, pour in the heavy cream and mix on low speed until just combined. Be careful not to overmix, as this can incorporate too much air.
Pour the cheesecake filling evenly over the cooled crusts in the muffin tin. Fill each cup until they are about 3/4 full.
Bake the mini cheesecakes in the preheated oven for 20-25 minutes, or until the edges are set but the centers are still slightly jiggly. They will firm up as they cool.
Remove the cheesecakes from the oven and let them cool in the pan for about 10 minutes. Then, carefully transfer them to a wire rack to cool completely. Once cooled, refrigerate for at least 2 hours before serving to allow them to set fully.