Slideshow SLIDESHOW: The Vegan Experience: Vietnamese Sandwiches with Tempura Sweet Potato and Avocado (Vegan Banh Mì)

[Photographs: J. Kenji Lopez-Alt]

Note: For the 32 days between February 1st and March 4th, I'm adopting a completely vegan lifestyle. Every weekday I'll be updating my progress with a diary entry and a recipe. For past posts, check here!

With over a week behind me, this year's Vegan Experience has been getting progressively more fun. I've passed the stage where I need to worry, "what the heck can I eat today?" and have moved squarely into the way cooler, "how can I make my lunch even more delicious than it already is?" phase. If you're a first-time vegan and still struggle, give it a bit of time. It takes a while to unlearn old habits and form all new ones, but pretty soon you'll be eying those vegetables the same way you used to peruse the meat aisle.

The difference? There's a lot more selection in the produce department, which can make lunch both exciting, and perhaps daunting. Sometimes its best to just make a selection and go with it. Tell yourself, "today, I'm going to focus my meal on sweet potatoes, come hell or high water." This kind of forced creativity can often lead to excellent end results.

Case in point: This sandwich, a Vietnamese-style banh mì made with tempura sweet potato and avocado, which I developed after saying those exact words to myself.

To be honest, I'd already been working on a good vegan version of the iconic Vietnamese sandwich. It shouldn't be too hard, right? I mean, most of the ingredients are already vegan to begin with. That's what fellow part-time-vegan Erin and I thought until we tasted every vegan sandwich offered at the three shops within a one-block radius of our office. Very few of them were tasty, and none of them were satisfying.

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I'd gotten to work, initially planning on using mushrooms in some form or another as my sandwich base, but I couldn't get anything that had the satisfying contrast of textures and flavors that a banh mí should have. I wasn't happy with any of the results, but it did mean that I had plenty of banh mì ingredients on hand. Once I got the sweet potato home, I put two and two together and a sandwich was born.

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As a part-time vegan, one of my biggest challenges is a lack of fat in my diet, which leaves me feeling a little unsatisfied unless I plan carefully.

In this case, rather than simply sauteing or steaming the sweet potato—which would lead to soft texture in a sandwich that already had some soft elements, I decided to batter it in a tempura-style batter before deep-frying it. This added not only a great crisp element to the mix, but also added some back some of that much-needed fat.

The key to a great tempura batter is to limit the amount of gluten formation in your batter. Gluten is the network of proteins that develops when flour mixes with water. It's desirable in sturdy baked goods like bread or pizza, but can cause a frying-batter to turn tough.

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To limit formation, I use a combination of regular wheat flour mixed with cornstarch (rice flour works too), and make sure to only mix my batter immediately before using it. Cornstarch and rice flour are both pure starches that contain none of the protein that can lead to toughness. In place of plain water, I use seltzer water, which contains bubbles of carbon dioxide that help keep things light. Keeping the seltzer ice fold will also help minimize gluten formation and lead to a light, crisp coating. For an even lighter, crisper batter, you can substitute part of the seltzer for ice cold vodka, which has the advantage of both vaporizing faster than water, and further limiting gluten formation.

When assembling the sandwiches, to really up the ante, I used a trick I learned at the awesome Banh Mì Ba Le in Dorchester, MA: add a ladleful of infused oil to the mix.

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The infused oil soaks into the bread ever so slightly, like in a good New Orleans muffuletta. I tried a few different combinations—lemongrass, basil, ginger, garlic, and scallions—but settled eventually on the classic Hainnanese pairing of ginger and scallions. Since I already had my oil hot for frying the potatoes, making the infused oil was as simple as pouring a ladleful of hot oil over a bowl full of sliced scallions and ginger, then seasoning it with salt.

When spread over the crisp sweet potatoes, it soaks into that crust, giving them a rich texture that is—dare I say—meaty?

The rest of the sandwich is pretty standard I always have a jar of homemade Viet pickled carrots and daikon (do chua) in my fridge for emergencies. To that I added spears of fresh cucumber, sprigs of cilantro, and slivers of jalapeño pepper. A drizzle of liquid aminos (such as Maggi or Bragg's) adds the umami factor.

The only missing element? The sweet mayo spread that adds a fatty, creamy texture to the mix.

Step 6: Eat

Last week Erin walked into the office and proclaimed that "avocados are like vegan butter." And she's absolutely right. Creamy, rich, and mildly flavored, they can add richness to most dishes without distracting from the main ingredient.

This was a helluva satisfying lunch.

With a fridge full of Banh Mì ingredients, I'm not stopping now on the filling front. My goal is to have a whole arsenal of fully satisfying vegan sandwiches to get into my regular rotation even once I return to my omnivorism.

Get The Recipe!

Vietnamese Sandwiches with Tempura Sweet Potato and Avocado (Vegan Banh Mì) »

Step-by-step instructions in the slideshow »

About the author: J. Kenji Lopez-Alt is the Chief Creative Officer of Serious Eats where he likes to explore the science of home cooking in his weekly column The Food Lab. You can follow him at @thefoodlab on Twitter, or at The Food Lab on Facebook.

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