Heat oven to 325°F. Toast walnuts on a sheet pan for 8-10 minutes, cool and then coarsely chop. Set aside.
Line a 13-by-9-inch baking pan with aluminum foil extending 2 inches over both short sides of pan. Grease foil and set aside.
Whisk butter, xylitol, eggs, and vanilla extract together in a large bowl. In another bowl whisk almond flour, guar gum, baking powder and cinnamon together. Stir into butter mixture until well combined. Stir in walnuts. Spread evenly into prepared pan. Bake until puffed and set, and a toothpick inserted in center comes out clean (top will not be browned), 40 minutes.
Cool completely in pan on a wire rack. Let stand until set, about 1 hour. The recipe can be prepared up to this point, covered with plastic wrap and stored at room temperature overnight.
Firmly gripping the foil on both ends, lift blondies out of pan, and place on work surface. Cut into 12 pieces and serve.