Before adding the maple syrup to the beaten eggs, it should be heated to 240 degrees. If you don’t have a candy thermometer, you can test by adding a drop of syrup to cold water; it should immediately form a soft ball. Be sure to buy only pure maple syrup, not a brand labeled “pancake syrup” or “maple-flavored syrup,” which is actually corn syrup flavored with maple extract. Pure maple syrup is graded according to color and flavor; grade B has a robust flavor that works well in baking and other recipes.

　　

Ingredients

makes 4 cups

　　6 large egg yolks

　　2 cups pure maple syrup, preferably grade B

　　1 pound (4 sticks) unsalted butter, chilled and cut into tablespoons

　　

Step 1

In the bowl of a standing electric mixer fitted with the whisk attachment, mix egg yolks on high speed until pale and thick, about 5 minutes.

　　

Step 2

Meanwhile, bring maple syrup to a boil in a saucepan over medium heat; clip a candy thermometer to side of pan. Cook until syrup registers 240°F, about 15 minutes. Remove from heat.

　　

Step 3

With mixer on medium speed, carefully pour the syrup in a slow, steady stream down the side of the bowl until it is completely combined, about 1 1/2 minutes. Continue mixing until the bottom of the bowl is only slightly warm to the touch, 5 to 6 minutes.

　　

Step 4

Add the butter, a few tablespoons at a time, mixing until completely incorporated after each addition. Once all butter has been added, scrape down sides of bowl with a flexible spatula, and continue beating until buttercream is fluffy, about 4 minutes more. Keep buttercream at room temperature if using the same day, or transfer to an airtight container and refrigerate up to 3 days or freeze up to 1 month. Before using, bring to room temperature and whisk on low speed until fluffy again, about 5 minutes.

　　Martha Stewart's Cupcakes