Chill your champagne glass.
In the bottom of a narrow container meant for an immersion blender, combine the juice from one ripe orange with eleven of the twelve raspberries (save one raspberry as a garnish).
Blend the freshly-squeezed orange juice with the fresh raspberries, until the mixture is smooth.
Strain the contents through a fish mesh strainer, to red rid of the pulp, and reserve the liquid.
*I use a fine mesh tea strainer. You could also use several layers of fine cheesecloth. Sometimes I strain the contents twice, cleaning the strainer in between, to get an even smoother final puree.
Add the chilled champagne to the bottom of the chilled champagne glass.
Add the fruit juice mixture that you strained earlier to the glass.
Mix very gently to combine.
Garnish with a fresh raspberry, and serve.