Swiss meringue/7-Minute frosting is light, fluffy, and sweet without being cloying. It also suited my purposes - I wanted something that would be sweet enough to help balance out the tart flavor of the curd without overwhelming it. Because a very specific shade of blue was requested and I didn't want to take any chances with that, I used water instead of juice and vanilla bean-scented sugar instead of vanilla extract in the frosting I made for the wedding cake and cupcakes. With only the vanilla to flavor it, the frosting is like a high grade of marshmallow fluff - smooth, shiny, and melting on the tongue. With the juice to flavor it, there is an additional layer of fragrance and flavor to dance on the tastebuds. Both are delicious! Best used the same day it is made; can be put into pastry bags [piping bags] and refrigerated for a day or two with minimal deflating. If there are leftovers, you can use them to make a pavlova: spread a layer about 1" [2.5 cm] thick on parchment paper and bake on a cookie sheet at 250 °F [120 ℃ or Gas Mark ½] for about 1 ½ hours. Turn off oven and let cool. Serve topped with lilikoi curd, whipped cream, and assorted chopped fresh fruit (I like pineapple and berries).
Lilikoi Frosting (adapted from classic 7-minute frosting - there are many recipes out there; I printed out Paula Deen's recipe from the Food Network website, used the same proportions, but changed up the instructions to be based on temperature and appearance).
One batch will frost a 9" 4-layer cake or 24 cupcakes.
2 large egg whites
1 ½ cups [165 g] granulated white sugar [UK: caster sugar works better as it will dissolve faster. US: if desired, first measure and then grind the sugar finer in a blender or food processor]
1 Tbs corn syrup [or 1/4 tsp / 1 g cream of tartar - if not available, you can leave this out; the frosting will then be less stable and should be served as soon as possible]
1/3 cup [80 mL] fresh lilikoi (passionfruit) juice (or lemon juice, or water)
pinch of salt
1 Tbs [15 mL] vanilla extract
With electric hand-held mixer, beat egg whites on low for 1 minute. Beat in remaining ingredients. In a bain-marie or double boiler, beat on high until temperature reads 140 °F [60 ℃], then continue to beat on high for 7 - 8 minutes until soft peaks will stand on the surface. Remove from heat and continue beating on low for 2 minutes. Should be fluffy, smooth, and glossy. If it begins to separate after cooling (water visible in bottom of bowl under the fluff), it is undercooked and can be re-beaten over hot water to get it completely cooked.
Update (August 2019): for those looking for a lilikoi glaze, it’s super easy:
Lilikoi Drizzle or Glaze
2 cups [8 oz or 226 g] confectioners sugar (also called icing sugar and powdered sugar - fine sugar with cornstarch)
2 - 4 Tablespoons [about 30 - 70 ml] fresh lilikoi (passionfruit) juice
Stir the lilikoi juice into the sugar a spoonful at a time, until it’s the consistency you want. For a drizzle that will sit on top of a cake, use 2 Tablespoons of juice. For a glaze that soaks into the cake, use more. I test it on a corner of a cake to see how thick or thin it is. The total amount will depend on things like how humid it is in the room you are working in and how warm the cake is. If you want the drizzle to stand up and hold its shape, make sure the cake is completely cool first!
It is currently lilikoi (passionfruit) season in Hawai'i, although it is getting close to the end - as of yesterday, Kokua Market still has some for sale (the farmers markets may have vendors selling the fresh fruit as well). I have been hoarding lilikoi pulp for months, getting fruit from my Mom Mom in Makaha and my hanai Mom in Manoa. Most of it got used for the wedding, but I do have some still stashed away. It won't last long, though. I've got a couple more recipes using lilikoi juice that are too good to save for special occasions!
Vegans: I'm working on a vegan lilikoi cupcake filling, and I'll post it when I get results I like. [update: never figured out a good curd, but now I have a jelly recipe using Pomonas Universal pectin - vegan and gluten-free - Lilikoi Lovers Passionfruit Jelly]
You really should use the freshest possible lilikoi juice for these recipes. About 5 - 6 fruits yield what I need for this curd recipe - I just cut them open (a serrated knife, like a breadknife or steak knife, works really well) and press the pulp through a mesh strainer. For a higher yield, heat the pulp up first, or give it a quick whirl in a food processor. If you have a Vitamix, you can blast the pulp, seeds and all, until smooth. This does NOT work well with a standard household blender - the broken seed pieces can be small enough to pass through a mesh strainer and still large enough to have jagged edges and be unpleasant to eat. The whole seeds are edible and in theory you could just leave them in - I did not want anyone at the wedding to bite into a cupcake and be alarmed by black spots in the center, though. If you can't get fresh, you can try frozen pulp (like Goya brand, available at many Latin/Hispanic markets) or Dafruta brand unsweetened passionfruit juice concentrate (also available in Latin/Hispanic markets - do not dilute, use it full strength. Mercado de la Raza in Honolulu carries it).
Lilikoi Curd Filling
makes about 2 cups [480 mL] - enough to ﬁll a 9" [23 x 3.5-centimeter] 3-layer cake or about 24 cupcakes
1/3 cup [70 grams] unsalted butter, at room temperature
3/4 cup [150 g] sugar
4 - 5 large egg yolks (4 for a softer, sauce-like curd, 5 for a thicker curd)
1 cup [250 mL] fresh lilikoi (passionfruit) juice
1 Tbs [15 mL] lemon juice (optional)
1/2 tsp [not sure how to convert this - a big pinch?] lemon zest (optional)
Cream butter and sugar together. Add remaining ingredients and blend. In a bain-marie (metal bowl set over pot of simmering water) or a double boiler, whisk frequently until
curd reaches 160 °F [71 ℃] (10 - 15 minutes). Curd will thicken further as it cools. Pour into bowl and press plastic wrap [cling ﬁlm] onto surface so "skin" will not form. Refrigerate until completely cooled before using. Use within 3 - 5 days. Keep refrigerated.