Marshmallow fluff and Baileys s’mores tart

Baileys s'mores tart

This is the third installment in a series all about egg whites. To catch up on how egg foams work and make chocolate-hazelnut meringues, go here. For more on the role of acid in egg foams and a recipe for blood orange pavlova, go here.

You know how everyone in the world starts any instructions for whipping egg whites with a strongly-worded warning about the dire consequences of getting even a speck or a smidgeon of fat into your foam? I’ve seen advice to throw out all of your whites if a yolk breaks while you’re separating the eggs, and I even warned all of you against using a plastic bowl to beat your meringue for the pavlova in case it’s holding on to traces of the deadly stuff. You’d think with all of the reading of egg-white-based recipes I’ve been doing lately this important tip would have sunk in.

Apparently not.

Stiff peaks

I was really excited to make marshmallow fluff at home, even more so when I was inspired to add a little Baileys–sounds delicious, right? And many meringue recipes call for alcohol for flavor, which means the internet thinks it’s a good idea. So my egg whites are whipping up beautifully, starting to hold their shape, and I throw in the magical Baileys.

Everything collapses. The delicate peaks revert to liquid. I’m pretty sure all hope is gone, but I keep whipping for a little while just in case. Nothing.  I looked again at the secret ingredient that betrayed me–Baileys Irish Cream. Oh right. Turns the two tablespoons of Baileys that I’d used to punch up the flavor added more than four grams of fat to the delicate foam.

Baileys and sunshine

So this week, as a lesson to myself and to prevent all of you from similar heartache, we’ll be exploring the effects of fat on whipped egg whites. It comes down to the basic kitchen principle that oil and water don’t mix. We’ve all seen a vinaigrette separate in its bottle, and this is the same idea.

I’ll leave the details of why oil and water don’t get along to another day and for now just stick to what this does to egg foams. We already know that an egg white foam has two parts: water from the egg whites and air bubbles introduced by all of the whipping. We also know that proteins unravel, interact with each other, and hold these two pieces together. One of the reasons this works has to do with the distinction between fat-like and water-like groups. Proteins are ginormous by molecular standards, so they’re big enough to contain both. The water-like areas are perfectly content to hang out in the watery bits of the egg foam, but the fat-like sections want none of that and flock to the air bubbles to get away from the water. The long proteins have a foot in both worlds so they bridge the water and the air, holding the bubbles in their matrix.

Whipped fluff

When a fat molecule comes along, it wants in on the air bubble space too. The proteins share their valuable real estate, so now some of the air-water border has proteins and some has fat. Unlike the proteins, though, fat is very one-dimensional and doesn’t have any water-like areas to connect it to the water part of the foam. The fat becomes a bridge to nowhere, clustering around the air bubble without tethering it to the water. As more fat takes up space around the air bubbles, it leaves less room for the fat-like sections of proteins, cutting off the bridge between air and water and making the foam collapse.

Moral of the story: you have to add Baileys to your marshmallow fluff in a different way.

Baileys s'mores tart

Marshmallow fluff and Baileys s’mores tart

Like a Swiss meringue, this marshmallow fluff starts by whipping egg whites and sugar over heat to partially cook the whites for stability and food safety. I paired with a simple graham cracker crust and a chocolate ganache–both spiked with Baileys!–for an easy St. Patrick’s Day-inspired treat. The fluff is also perfect with peanut butter (I may have had a fluffernutter pancake last week, it may have been amazing) and makes an excellent frosting.

Yield: one 9-inch tart plus about 2 cups extra fluff

Marshmallow fluff:

3 egg whites

¾ c. sugar

½  t. cream of tartar

¼ t. salt

1 t. vanilla

Graham cracker crust:

1 sleeve graham crackers (9 sheets)

5 T. butter, melted

2 T. Baileys

Baileys chocolate ganache:

½ c. heavy whipping cream

1 c. dark or semi-sweet chocolate chips

1 ½ T. Baileys

1 t. coconut oil

Make the marshmallow fluff:

Combine the egg whites and sugar in the bowl you’ll whip them in (your upright mixer bowl or another metal bowl if you have a handheld mixer). Place the bowl over a pot of boiling water to create a double boiler and make sure the water does not touch the bottom of the bowl. Heat, stirring continuously, until the mixture is frothy and steaming.

Using an electric mixer, quickly start to whip the hot egg whites on medium speed. Add the cream of tartar, salt, and vanilla. Increase to high speed and continue to whip until the mixture is thick enough to hold its shape and the bowl feels cool.

Make the graham cracker crust:

Preheat the oven to 350 degrees F. Butter a 9-inch cake pan (or a tart pan, if you have one of those).

Crush the graham crackers in a food processor or with a plastic bag and a rolling pin. In a large bowl, mix in the melted butter and Baileys. The mixture should look like wet sand and should hold together when you pinch it. If it seems too crumbly, add another teaspoon or two of butter.

Press the mixture into the prepared pan. Bake until the top has lost its sheen and the edges brown slightly. Let cool.

Make the Baileys ganache:

Heat the cream in the microwave until it steams, using 30-second increments (it took four in my microwave). Add the chocolate chips and stir until melted. While it is still warm, stir in the Baileys and coconut oil.

Assemble the tart:

Spread the ganache over the top of the graham cracker crust, leaving a thin border around the outside. Spoon marshmallow fluff onto the middle of the tart and use a warm offset spatula or the warm back of a spoon to spread it out and create swirls and peaks. To brown the fluff, place it under the broiler for a minute or two, keeping a close eye on it and rotating it if necessary.

Fluff recipe adapted from Bon Appetit, ganache adapted from Life Tastes Like Food.

Baileys s'mores tart