In a medium saucepan over medium heat, combine 1 cup of finely diced fresh strawberries and 1/4 cup granulated sugar. Cook for about 45 minutes, stirring occasionally and mashing the strawberries halfway through, until the mixture thickens and becomes jam-like. Once done, set aside to cool while you prepare the filling.

In a mixing bowl, combine 8 oz of softened cream cheese, 1/4 cup granulated sugar, and 1/2 teaspoon vanilla extract. Beat with an electric mixer on medium speed until the mixture is smooth and creamy, about 2-3 minutes. Divide this cream cheese mixture into 18 portions, flatten them gently, and place them on a baking sheet. Freeze until solid, around 30-40 minutes.

In a large bowl, use an electric mixer to beat together 1 cup of softened unsalted butter and 1 cup of granulated sugar until light and fluffy, 3-5 minutes. Add 1 large egg and 1 teaspoon vanilla extract, mixing until the dough is pale and voluminous. This will serve as the base for your soft strawberry cheesecake cookies.

In a separate bowl, whisk together 3 cups of all-purpose flour, 1/2 teaspoon baking powder, and 1/4 teaspoon salt. Gradually fold this dry mixture into the butter mixture, using a spatula or wooden spoon until just combined. Be careful not to overmix; the cookie dough should remain soft and slightly sticky.

Divide the dough into equal portions, and flatten each piece into a disk. Place a frozen cream cheese filling in the center and layer with about 1 tablespoon of homemade strawberry jam. Fold the dough over to enclose the filling completely, shaping it into a ball to create your soft strawberry cheesecake cookies.

Preheat your oven to 350°F (175°C) and line two baking sheets with parchment paper. Place the cookie dough balls on the prepared sheets, spacing them a few inches apart. Bake for 11-12 minutes, or until the edges are lightly golden. Let the cookies cool on the baking sheet for about 10 minutes before transferring them to a wire rack.