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1
For the buttercream: Bring the rum and cane sugar to a boil in a medium saucepan.
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2
Add the raisins, remove from the heat, and let macerate for at least 4 and up to 24 hours at room temperature.
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3
Strain the raisins, finely chop, and set aside for the cupcake batter.
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4
Bring the strained rum to a boil in a small saucepan and reduce to 1/4 cup.
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5
Remove from the heat and let cool before adding to the buttercream.
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6
Combine the butter and cream cheese in the bowl of a stand mixer fitted with the whisk attachment, and whip until light and fluffy, scraping the sides and bottom of the bowl once.
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7
Add 3 cups of the powdered sugar and whip until light and fluffy.
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8
Add the cooled reduced rum and the rum extract and add more powdered sugar, 1/4 cup at a time, and whip until slightly thick, spreadable consistency.
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9
For the cupcakes: Adjust the oven rack to the middle position and preheat the oven to 350 degrees F. Fill mini muffin tins with liners and spray the liners with nonstick spray.
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10
Whisk the flour, baking powder, baking soda, salt, 1 1/2 cups of the sugar, cinnamon, allspice, and nutmeg together in large bowl.
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11
Whisk together the melted butter, buttermilk, oil, vanilla, rum extract, and yolks in a medium bowl.
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12
In a clean bowl of a stand mixer fitted with the whisk attachment, beat the egg whites at medium-high speed until foamy, about 30 seconds.
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13
With the machine running, gradually add the remaining 1/4 cup sugar; continue to beat until stiff peaks just form, 30 to 60 seconds.
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14
Transfer to a separate bowl and set aside.
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15
Wash the bowl and dry.
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16
Add the flour mixture to the now-empty mixing bowl fitted with whisk attachment.
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17
With mixer running at low speed, gradually pour in the butter mixture and mix until almost incorporated (a few streaks of dry flour will remain), about 15 seconds.
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18
Stop the mixer and scrape the whisk and sides of the bowl.
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19
Return the mixer to medium-low speed and beat until smooth and fully incorporated, 10 to 15 seconds.
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20
Using a rubber spatula, stir 1/3 of the whites into the batter to lighten, and then add the remaining whites and gently fold into the batter until no white streaks remain.
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21
Quickly fold in the reserved raisins.
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22
Fill the cupcake molds 7/8 full and bake until just firm, about 10 minutes.
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23
Let cool in the pan set on a baking rack for 5 minutes.
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24
Remove the cupcakes from the tins and let cool completely on the racks.
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25
Frost with the rum raisin buttercream.
