Chocolate Cream-Filled Sandwich Cookies

In a medium saucepan over medium-low heat, whisk together the heavy cream and cream cheese until the cream cheese is melted and combined. Remove from the heat and add the white chocolate, stirring until melted and smooth. Transfer the mixture to a large bowl and cool for 10 minutes. Cover and refrigerate until chilled, about 2 hours. Meanwhile, heat oven to 350 degrees F. Line 2 baking sheets with parchment paper. In a bowl, whisk together the flour, cocoa, baking powder, baking soda, and salt. Using an electric mixer, beat the butter and sugar in a large bowl until light and fluffy; beat in the egg and the vanilla. Reduce the mixer speed to low and gradually add the flour mixture, mixing just until combined. Drop level teaspoon of dough onto the prepared baking sheets, spacing them 1 1/2 inches apart. Bake until firm around the edges but slightly soft in the center, 8 to 10 minutes. Let cool on the sheets for 5 minutes, then transfer to a wire rack to cool completely. Using an electric mixer, beat the chilled white chocolate filling until fluffy, about 2 minutes. Spoon the filling into a large resealable freezer bag. Snip a 1/2-inch opening off one corner of the bag; pipe the frosting on half the cookies, then sandwich with the remaining cookies.