Preheat oven to 350 degrees. Line or spray an 8 x 8 inch cake pan
In a large mixer bowl whisk together almond flour, coconut flour, baking powder, salt, and brown Swerve until no lumps remain
Add softened butter. Beat on low 10 seconds then on medium for 30 seconds or until everything is fully combined
Add egg and vanilla extract. Beat on low for another 10 seconds then on medium for 30 seconds more or until the batter is smooth
Scrape down the sides of the bowl and push all the batter to the center of the bowl. If desired fold in 1/4 cup of add-ins (nuts, butterscotch chips, white chips etc)
Scoop mixture into prepared cake pan and spread it evenly throughout the pan.
Bake at 350 degrees for 20-25 minutes or until golden around the edges. The blondies will be soft but will firm up as it cools
Let cool in the pan for 30 minutes. Use a butter knife and loosen the edges of the cake from the sides of the pan
Let cool 30 minutes more or until completely cooled.
Cut into desired size bars. Store leftovers in an airtight container at room temperature