I’ve been kind of obsessed with flower everything on my cakes these days. Real or buttercream, I love them all. I actually made this cake back in May, and by the time I got to editing photos it was the peak of summer. And because the filling is sweet potato pastry cream, it just didn’t go with the season. But now that it is on the cusp of fall, I feel like it’s appropriate to post this. (Although, personally, this is my favorite pastry cream of all time and I love it any time of the year.)
The star of this cake is the sweet potato, but not the orange fleshed kind but the purple skinned, yellow fleshed kind. This type of sweet potato is popular in Korean desserts and tastes similar to a roasted chestnut. In the past, I’ve also featured this type of sweet potato in this post: Mini Green Tea Cake.
If you’ve never made pastry cream before, my advice for you is to go slow with pouring the hot milk into the egg mixture, as in a slow drizzle, not a pour. You want to avoid curdling at all costs. But if you do it right, man oh man is it worth it. Gone are the days of powdered mixes. You will never look back. Fill it between your favorite vanilla cake and watch the compliments roll.
As for the decoration, I’ve always loved ranunculus and decided to try to pipe it. It is easier than It looks but is quite time consuming to pipe each flower, especially since they have so many petals. Here are the steps to pipe the flower:
- Cut out many squares of parchment or wax paper. You will use one square per flower. (I usually cut mine around 3×3 inches.)
- With a flower nail in your hand, pipe a small amount of frosting onto the center of it. (As shown in Photo 2.)
- Place a piece of parchment paper on top of the frosting. (As shown in Photo 3.)
- Using a small round tip (wilton #2 or #3), pipe a small amount of green frosting in the center of the flower nail in a round, circular shape. (As shown in Photo 4.)
- In a piping bag filled with light green frosting and fitted with a petal tip with the wider side facing the flower nail (wilton #102, or larger pending on the size of the flower you want to pipe), pipe a square around the circle, overlapping each other on the ends. (As shown in Photo 5.)
- In a piping bag filled with light pink frosting and fitted with a petal tip with the wider side facing the flower nail (wilton #104, or larger pending on the size of the flower you want to pipe), pipe 5 dashes around the light green square overlapping the ends. (As shown in Photo 6.)
- Using the same piping bag, pipe 6 dashes around the pink circle. You want to show a little bit of the circle beforehand to create an illusion of overlapping petals. (As shown in Photo 7.)
- Continue piping dashes along the outer edge of the flower, increasing the number of dashes by 1 until you reach the size of the flower you desire. (As shown in Photo 8.)
Sweet Potato Pastry Cream
3 medium sized Korean sweet potatoes, roasted and peeled.
2 c. whole milk
½ c. sugar, divided
2 egg yolks
1 egg, large
¼ c. cornstarch
a pinch of kosher salt
2 tbsp. unsalted butter
1 tsp. vanilla extract
- In a food processor, mix the sweet potatoes until a smooth puree forms. Set aside.
- In a medium saucepan, whisk the milk and ¼ c. of sugar and heat until the milk boils.
- While the milk heats, grab a medium bowl and whisk together the egg yolks, egg, ¼ c. sugar, cornstarch and the salt until smooth.
- Once the milk is heated, slowly drizzle in the milk mixture into the egg mixture with one hand while whisking the egg mixture with the other. Once the milk is completely incorporated into the egg mix, return the entire mixture into the saucepan.
- Heat the saucepan while whisking until the mixture becomes thickened like pudding.
- Take it off the heat and stir in the butter and vanilla extract.
- Mix the sweet potato with the pastry cream until homogenous.
- Place a piece of plastic wrap directly onto the pastry cream and refrigerate until cool and set. (about 4 hours, or overnight)