1. Preheat oven to 350°F. Lightly grease six 3-inch tart pans.
2. For the pumpkin layer, whisk together the melted butter, sugar, vanilla, pumpkin purée, and egg yolk. Stir in the flour and pumpkin pie spice until smooth. Set aside.
3. For the cookie dough, stir together melted butter, brown sugar, and granulated sugar. Mix in the egg yolk, milk, and vanilla. Add flour, baking soda, and salt, stirring just until combined. Fold in chocolate chips.
4. Divide cookie dough between the tart pans and press into a thin, even layer across the bottom and halfway up the sides.
5. Spoon pumpkin filling into the center, leaving a small cookie border around the edges.
6. Bake for 18–20 minutes, until the cookie edges are golden and the pumpkin center is just set.
7. Cool in the pans for 15 minutes, then remove. Top with whipped cream and a sprinkle of pumpkin pie spice or flaky sea salt, if desired.
