For Cupcakes:

1. Preheat oven to 350 degrees. Line two standard muffin pans with paper liners. Set aside. Whisk together flour, baking powder, salt, and cinnamon in a medium bowl; set aside.

2. Put butter and sugar in the bowl of an electric mixer fitted with the paddle attachment; cream on medium-high speed until pale, 2 to 3 minutes. On medium speed, add eggs one at a time, mixing well after each addition. Add vanilla and mix, scraping down sides of bowl. With the mixer on low speed, add the flour mixture in three batches, alternating with two batches of milk. Stir with a rubber spatula until the batter is evenly blended.

3. Divide batter evenly among lined cups, filling each two-thirds full. Bake until a cake tester inserted into centers comes out clean. 15 to 18 minutes, rotating pans halfway through.

4. Let the cupcakes cool in tins on wire racks 20 minutes. Invert cupcakes to remove from pans. Cool completely on racks before frosting.

For Frosting:

In the bowl of an electric mixer fitted with the whisk attachment, beat the egg yolks on high speed until light and fluffy, about 5 minutes; set aside. In a small saucepan set over medium-high heat, bring the maple syrup to a boil, and cook until it registers 240 degrees on a candy thermometer, about 15 minutes. Remove from heat.

With the mixer running, slowly pour syrup down the side of the bowl in a slow steady stream, until completely incorporated, about 1 minute. Continue beating until bowl is just slightly warm to the touch, 4 to 5 minutes. Add butter, one piece at a time, until thoroughly incorporated and the frosting is fluffy, about 4 minutes. Frost cinnamon cupcakes and top with crumbled bacon.