Special equipment: a standard 12-cup muffin tin, 12 paper cupcake liners, a pastry bag fitted with a star tip, a deep-frying thermometer and cookie cutters
For the cupcakes: Preheat the oven to 350 degrees F. Line a standard 12-cup muffin tin with paper cupcake liners.
In a medium mixing bowl, combine the flour, cinnamon, baking soda, baking powder and salt. Set aside.
In the bowl of an electric mixer, cream the butter, granulated sugar, light brown sugar, sour cream, vanilla and eggs until fluffy, about 3 minutes. Turn the speed to low and add the dry ingredients. Blend until well combined, about 25 seconds.
Pour 2 1/2 to 3 tablespoons of batter into each cupcake liner. Bake the cupcakes until a tester inserted into the center comes out clean, about 20 minutes. Let cool.
For the buttercream: Using an electric mixer with the paddle attachment, cream the butter, vanilla and cinnamon until smooth, scraping down the sides as needed, about 2 minutes. With the machine running on low, add the powdered sugar 1 cup at a time, alternating with the milk, and mix until combined. Fit a pastry bag with a star tip and fill with the buttercream.
For the tortilla crisps: Mix together the granulated sugar and cinnamon on a large plate. Set aside.
In a medium, heavy-bottomed saucepan, add enough oil to come halfway up the sides of the pan. Heat over medium-high heat until a deep-frying thermometer inserted in the oil registers 350 degrees F. (If you do not have a thermometer, test the oil with a piece of tortilla, which should sizzle when it touches the oil and should brown in 2 to 3 minutes.)
Meanwhile, using a cookie cutter, cut the tortillas into different shapes and/or letters. Fry the tortilla pieces until golden brown, 2 to 3 minutes. With a slotted spoon, transfer the crisps to paper towels to drain. While still warm, transfer to the cinnamon-sugar mixture and turn to coat.
To assemble the cupcakes: Pipe a swirl of buttercream on each cupcake and top with a tortilla crisp.