Preheat oven to 300°F.
Center rack in the oven. Line an 8-inch square baking pan with foil, butter the pan and place it on a baking sheet.
Whisk the flour, salt, pumpkin pie spice, and cinnamon together. Put the chocolate in a heatproof bowl, and set the bowl over a saucepan of simmering water. Stir occasionally until the chocolate melts. Remove the bowl from the saucepan and add the butter, stirring until it melts. It's important that the chocolate and butter not get very hot. However, if the butter is not melting, you can put the bowl back over the still-hot water for a minute. If you've got a couple of little bits of unmelted butter, leave them - it's better to have a few bits than to overheat the whole.
Working with a stand mixer fitted with the whisk attachment, or with a hand mixer in a large bowl, beat the eggs and sugar until thick and pale, about 2 minutes. Reduce the mixer speed and pour in the chocolate-butter mixture, mixing only until it is incorporated- you'll have a thick, creamy batter.
Add the dry ingredients and mix at low speed for about 30 seconds - the dry ingredients won't be completely incorporated. Then finish folding in the dry ingredients by hand with a rubber spatula. Scrape the batter into the pan.
Place the unwrapped kisses in a microwave-safe bowl and microwave on HIGH for 1 minute. Stir until smooth, and then drop by spoonfuls into the brownie batter. Using a knife, swirl the batter to create a marbled effect.
Bake for 50 to 60 minutes, or until the top is dry and crackled and a thin knife inserted into the center comes out clean. Depending on your oven, this may take longer to bake. Transfer the pan to a rack and cool to warm or room temperature.
Carefully lift the brownies out of the pan using the foil edges as handles and transfer to a cutting board. Remove the foil and discard. Cut the brownies into 16 squares.