Whisk together the oat flour, millet flour, sweet rice flour, tapioca starch, sugar, xanthan gum, and salt in a large bowl.

Add the cold butter and working quickly with your hands, break up the butter into the flour until the largest pieces are about the size of an almond.

One tablespoon at a time, dribble in the ice water, combining with a fork or your hands each time, until the dough holds together when pinched with your fingers (add water until it just holds together, but is not sticky. If you need more water, add a teaspoon at a time). Knead the dough until it just comes together. Divide the dough in two.

Dust your work surface lightly with millet flour and roll each piece out into a ¾-inch thick rectangle. Dust the top of the dough lightly with millet flour and Fold the dough into thirds like a letter and then in thirds once again to form a square. Repeat. Press the dough into a 1-inch thick rectangle. Wrap each piece in plastic and chill for an hour or up to overnight.

Meanwhile, prepare your strawberry jam, as instructed below) if using homemade.

Dust your work surface slightly with millet flour. Remove one portion of dough from the refrigerator and let sit for 5-10 minutes to soften. Carefully roll into a 9x12-inch rectangle, dusting with millet flour and flipping to keep it from sticking. Repair any cracks as you roll.

Cut into 9 rectangles, 3x4 inches each, and stack them on a plate in the refrigerator while you repeat with the second portion of dough. If desired, reroll any scraps of dough to make an additional 4x6 rectangle and cut into two smaller 3x4 rectangles.

Brush egg over the entire surface of a rectangle of dough and place 1 heaping tablespoon chilled strawberry jam in the middle. Carefully place a second rectangle on top and press the edges to seal, being careful not to press the jam out of the sides. Use the tines of a fork to crimp the edges. Repeat with remaining rectangles, laying each on a parchment-lined baking sheet about 1-inch apart, as you go. Try not to worry if some of the tops crack just a little - you'll cover them in icing and hide any imperfections.

Use the end of a chopstick or thick skewer to poke 9 holes in the top of the pastry.to vent out the steam. Chill the pop tarts for 15 minutes while you preheat the oven to 400°F. When the oven is done preheating, brush the top of each pop tart with heavy cream, milk, or the remaining egg wash (the egg wash will make the pop tarts a little more shiny and golden than pictured).

Bake for 39-42 minutes, until the tops are golden brown and crisp. Remove from heat and using a clean cloth, paper towel, or flat spatula, gently press the pop tarts down to remove any steam and flatten them a bit. Let cool completely before icing.

Put 1-2 teaspoons of glaze on a pop tart and use a spoon to gently spread it around. Top with sprinkles and repeat with remaining pop tarts.

If using frozen strawberries, puree them in a blender until completely smooth. If using fresh strawberries, puree them with ¼ cup water until smooth. Press the puree through a fine mesh sieve into a pot. Whisk the sugar and cornstarch together until combined then add it to the pot along with the lemon juice. Bring it to boil over medium heat, then reduce heat to a low simmer.

Bring water to boil and add hibiscus leaves. Steep for 10 minutes until deep dark red then strain out the tea leaves and chill until room temperature (Use the freezer to speed this up!).

Add honey and 1½ tablespoons of the brewed hibiscus tea concentrate to the powdered sugar and whisk until smooth. Slowly add more tea, as needed, until it becomes a smooth thick glaze that holds its shape when drizzled onto itself for a few seconds before incorporating back in.