2 teaspoons vanilla bean paste or 1 teaspoon vanilla extract
Milk, as needed
At least an hour before starting the dough, toss the rhubarb with two tablespoons of sugar. Let sit at room temperature, stirring occasionally.
When ready to make the dough, tip the rhubarb into a fine-meshed sieve set over a bowl. Leave to drain completely, reserving the liquid.
In a decent-sized bowl, whisk together the flour, remaining three tablespoons of sugar, baking powder, salt, and baking soda. Using the large holes on a box grater, shred the butter over the dry mix. Gently toss the butter strands through the flour with a fork until coated. Chill for 10 minutes.
Make a well in the centre of the flour mixture, and pour in the sour cream, milk, and vanilla bean paste. Using a fork, bring the dry ingredients into the wet, to make a loose dough with dry flour remaining. Tip everything out onto a clean work surface, and using a bench scraper or clean hands, knead the dough until it holds together, packing any dry flour into the dough, then folding the dough over itself to incorporate. If the dough is too dry, flick on milk as needed. If damp, dust with flour. With a lightly-floured pin, roll the dough to a rectangle about a quarter-inch (six mm) thick.
In a clean bowl, toss the drained rhubarb with a little flour to absorb any juices. Scatter half the rhubarb over one side of the dough, leaving a border on the sides. Fold to encase the fruit, then roll out again, repeating the process with the rest of the rhubarb. Chill dough for 10 minutes.
Line a plate with paper towels, and set a baking rack over a parchment-lined sheet pan. Pour oil to a depth of about two inches (five cm) in a heavy, high-sided pot or Dutch oven with a deep-fry thermometer clipped to the side. Preheat the oil to 350°F (175°C) over medium heat.
On a lightly floured surface, cut the dough in half. Refrigerate one piece. Roll the other piece into a four-by-six-inch rectangle. Portion into six two-inch squares using a two-inch biscuit cutter or sharp knife. Pressing lightly, score a smaller square into the top of each piece with a one-and-a-half-inch cutter, or make a shallow slash with a thin knife (these cuts will aid in even frying).
Gently lower the fritter into the hot oil. Fry the fritters three to four at a time, depending on the size of your pot and keep an eye on maintaining the oil temperature. Turn after one minute, then cook for one minute on the second side. Continue to cook, turning as needed, until golden brown and light for their size, around four minutes total. The fritters should have an internal temperature of 180°F. Drain on both sides on paper towels before moving to the baking rack.
While the first fritters fry, roll and cut the remaining dough.
Make the glaze by whisking rhubarb strained juice, confectioner's sugar, kosher salt, vanilla bean paste and vanilla extract together, and adding milk as needed to make a pourable glaze — it should be about the consistency of cream.
Dunk the still-warm fritters into the glaze, then return the enamelled beauties to the rack to set completely. The fritters are best the day they are made. TIP: Add grated nutmeg or lemon zest to the dough for an aromatic hit. Enjoy!