- With a stand electric mixer, beat egg yolks on high until light and fluffy, about 5 minutes.
- Meanwhile, pour maple syrup into a medium saucepan over medium-high heat. Bring syrup to a boil and cook until a candy thermometer registers at 240F, just above the soft ball stage and about 15 minutes.
- Remove saucepan from heat.
- While the stand electric mixer is running, pour syrup in a slow, steady stream down the side of the mixing bowl and into the egg-yolk mixture. Please Note: it is essential that the syrup touches the side of the bowl while being poured into the mixing bowl. This allows the sugar to be more evenly incorporated and not splatter onto every side of the bowl. Continue until the syrup has been completely incorporated, about 1 1/2 minutes.
- Beat until the bowl is just slightly warm to the touch, 5 to 6 minutes.
- Add butter, one piece at a time, until all has been completely incorporated and the frosting is fluffy, about 4 minutes more.
- To frost the cake after it has completely cooled, remove the cake from the pan and cut in half. Frost the bottom half of the cake. Place the top half of the cake back on top of the bottom half. Frost the top of the cake and serve!
Recipe by Season Johnson at https://www.seasonjohnson.com/birthday-celebration-breakfast-sandwich-chocolate-cake/