Preheat your oven to 350°F (175°C). In a mixing bowl, combine crushed digestive biscuits with melted unsalted butter, pressing firmly into the base of a springform pan. Bake for 10 minutes, then cool.

In a large bowl, beat softened cream cheese and granulated sugar until smooth. Add eggs one at a time, mixing well after each addition. Stir in vanilla extract and set aside.

Pour the cream cheese filling over the cooled biscuit base, spreading evenly. Bake for 45 minutes; the edges should be set but the center slightly jiggly. Cool to room temperature, then refrigerate for at least 4 hours.

In a saucepan, combine sweetened condensed milk, brown sugar, and unsalted butter over medium heat. Stir for about 10 minutes until thickened to a golden caramel. Cool slightly before pouring over the chilled cheesecake.

Refrigerate for at least 1 hour to set the caramel topping. Carefully remove the sides of the springform pan and serve.