Preheat oven to 350 degrees Fahrenheit and lightly grease the indents in the muffin pan.
For the streusel, use a fork to combine the flour, brown sugar, granulated sugar, oats, pinch of salt and softened butter into coarse crumbs.
For the pumpkin filling, in the bowl of an electric mixer, cream together egg, pumpkin puree, pumpkin pie spice, heavy cream and brown sugar.
Press 1 Tbsp. of the streusel mixture in the bottom of about 15 muffin tins. Spread 1 heaping Tablespoon pumpkin filling over the crust. Top with 1 Tbsp. streusel mixture. Repeat with remaining mixture until it's gone.
Bake for approximately 18-20 minutes, or just until set. Let them cool in the pans until they are easy to release (try after 15-20 minutes). Use a butter knife to run it around the edges and release the cookies. Then carefully remove them from the pans.