Square Root Tart with Horseradish Custard (Gluten-Free)

If you follow my blog, you probably already know about Pi Day.. but did you know about Square Root Day? It’s on April 4th this year – 4/4/16, of course!

Far from a yearly thing, square Root Day only comes around a few times in ones lifetime … so it’s fun to do something to acknowledge it. The next one won’t be til 2025, after all! As numbers nerds, it’s always fun to translate that into food, as an event. Things like this – and Pi Day – are fun. It’s a great way to bring people together without it being a BIG ordeal, like some of the larger holidays.

This square root day is especially fun for us, because it happens to fall on my husband’s birthday. So, I decided to make him a very special recipe to commemorate it. After much thought, I settled on this, a square root tart.

Roasted root veggies are one of my husband’s favourite foods, and I can’t blame him – LOVE them, myself. I decided that it needed to incorporate a “root” themed custard, so I went with horseradish. The slight bite of the creamy custard is a great foil for the texture and earthiness of the root veggies. Where I usually use cornstarch for certain things in crust recipes, I substituted potato starch… while potato is technically a tuber – not a “real” root – it’s closer to being on theme than corn starch is! 🙂

If you aren’t gluten-free (and won’t be serving this to someone who is!) you can substitute any single crust pie crust recipe, or a store bought one. We used a 9″ x 9″ square tart pan.

If you ARE gluten-free (or know someone who is)… you should be sure to check out my Kickstarter Campaign for Beyond Flour 2!


Square Root Tart with Horseradish Custard

1/2 cup buckwheat flour
1/4 cup white rice flour
1/4 cup millet flour
1/4 cup sweet rice flour
1/4 cup potato starch, plus extra for rolling
3/4 tsp xanthan gum
1/4 (4oz) brick cream cheese
1/4 cup cold butter
1 egg
2 Tbsp cold water

1 large carrot
1 medium parsnip
1 small rutabega
1 medium small turnip
1 small golden beet
1 small red beet
Pan spray
Salt and pepper

2 Tbsp Butter
2 clove Garlic, pressed or minced
1 Tbsp horseradish
1/2 cup Dry white wine
1 Tbsp potato starch
4 Large egg yolks
1/2 cup milk
Salt and pepper

Measure flours, potato starch, and xanthan gum into the bowl of your food processor, blitz to combine. Add cream cheese, butter, and egg, blitz a few times until mixture resembles gravel. Stream in cold water as you run the food processor, just long enough to start to bring it together as a dough – you may need to use a little more or less water. Do NOT over-process it!

Remove dough from processor, knead lightly to bring it together as a ball. Wrap in plastic film, chill for 1 hour.

Preheat the oven to 400 degrees F.

Generously dust work surface with potato starch, Roll chilled dough out to a rough square that’s slightly bigger than 11″ x 11″. Carefully transfer rolled dough to tart pan, smoothing the bottom and pressing the dough into the sides of the pan. Trim any excess dough that extends past the top of the pan, prick the flat (bottom) surface of the crust a few times with a fork.

Bake for 20 minutes or until golden brown. Remove from oven and allow to cool. Turn oven down to 350F.

While baking the crust, prepare your roasted roots.

Line 2 large baking sheets with parchment paper, spray with pan spray.

Peel all vegetables except for the beets. Carefully slice them into 1/4″ thick rounds – we use a mandoline slicer for this. Arrange onto one of the prepared pans, spray with pan spray.

Repeat with golden beets, arranging on one half of the second prepared pan. Repeat with red beets, arranging on the remaining space on the second pan. (Fussy, I know.. but beets “bleed” like crazy!). Sprinkle veggies on both pans with salt and pepper. Roast until tender, about 30 minutes.

As veggies are roasting, prepare your custard:

In a small saucepan, melt butter over medium heat. Add garlic, horseradish, and white wine, whisk until smooth; gently bring to a simmer.

In a small bowl whisk together potato starch and egg yolks until smooth. Add milk, continue whisking until smooth. Add milk mixture to pot, simmer over medium heat until very thick. Once custard has thickened to your liking, remove from heat.

Spread hot custard in crust, top with roasted root veggies, serve immediately.

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