In a mixing bowl, whisk together sour cream, eggs, milk and oil until well combined.

In a food processor, blitz together starches, flours, xanthan gum, baking powder, and salt until well combined.

Add butter, blitz until mixture resembles gravel.

Add wet mix, blitz just long enough to allow a sticky dough to come together.

Wrap dough in plastic film, allow to rest on counter for 45 minutes.

While waiting, work on the filling:

Finely chop pepperoni, place in a bowl with shredded cheese, stir to combine.

Add just enough pizza sauce to barely bind the ingredients together.

Wrap with plastic, chill until use.

Line a baking sheet with parchment paper, set aside. Dust work surface lightly with corn starch.

Roll dough out very thin - about ⅛ of an inch thick.

Using a pizza wheel or sharp knife, cut dough into 1.5" wide strips. Cut those strips into 4" long pieces.

Place about 1 teaspoon of filling in the middle of each piece.

Whisk together egg and water, use a pastry brush to paint a thin line of egg mixture along all 4 edges of each piece.

Fold the two short ends in to the middle, overlapping slightly. Press down on all edges, taking care to push out any excess air.

Transfer all pizza rolls to baking sheet.

Get a large pot of water JUST to the point of gently bubbling - you don't want violent bubbles, or it'll rip apart your rolls.

In small batches, poach the pizza rolls just until they float.

Transfer cooked rolls back to the baking sheet to drain off.

Heat oil to 350 F (180 C). Line a clean baking sheet with 2 layers of paper towels.

You can use a deep fryer, or a heavy pan. If not using a deep fryer, use a deep, heavy pot, filled to at least 2" deep.

Once oil reaches temperature, carefully fry pizza rolls in small batches until nicely browned and crispy.

This should take about 1-2 minutes per side.

Transfer fried pizza rolls to baking sheet to drain, serve hot.