In a medium bowl, whisk together Calla's gluten-free flour blend, gluten-free oat flour and xanthan gum.
Cut in butter until particles are the size of small peas. Sprinkle 2 tablespoons water over flour mixture; mix with fork.
Gather pastry into a ball; divide into halves. Pat each half into a 12x3 inch long rectangle on an ungreased cookie sheet. Rectangles should be about 3 inches apart.
Topping:
In a small bowl, whisk together Calla's gluten-free flour blend and gluten-free oat flour.
Heat butter and water to a rolling boil; remove from heat.
Quickly stir in almond extract and flour mixture. Stir vigorously over low heat until mixture forms a ball, about 1 minute; remove from heat.
Add eggs; beat until smooth and glossy. Spread half of the topping over each rectangle.
Bake until topping is crisp and brown, about 50 minutes; cool. (Topping will shrink and fall, forming the custardy top).
Powdered Sugar Glaze:
Mix together powdered sugar, vanilla and almond extract.
Stir in warm water, 1 teaspoon at a time, until smooth and of desired consistency.
Assembly:
Spread pastries with powdered sugar glaze; sprinkle with nuts.
Makes 2 Coffee Cakes (5 to 6 servings each).
Notes
Gluten-free Oat Flour can either be purchased or can be made by using your high-speed blender to grind up gluten-free oatmeal.