Preheat oven to 350°F and line 12x16 inch baking sheet with partment paper.
Combine spinach, egg yolks, salt and blen with immersion blender or in a food processor until everything is fully mixed.
Add all-purpose gluten free flour to the spinach mixture and mix until combines.
In a separate bowl beat on a high speed 3 egg whites until stiff peaks, about 2 minutes.
Add aout ⅓ of egg whites to the spinach mixture and refully fold it in. Then add the rest of egg whites and fold them in with spatula. Do not overmix.
Spread the mixture evenly on the sheet, about ½ inch thick and bake for 10 minutes.
Combine cream cheese, sour cream, milk and lemon juice.
Once the sponge is done abking, take is out of the oven and let it cool completely. Once it is cooled, use a cutting board to flip it and carefully remove partchment paper, then flip it back.
Spread the cream cheese mixture on the top of the sponge. Next, layer thin slices of smocked salmon. Leave about 1 inch from the bottom of the horizontal side without salmon, to make sure the roll holds its shape better.
Start rolling the sponge from the top of the horizontal side, then wrap it in the cling wrap an leave it in the fridge for at least 2 hours.
When ready to serve, take is out of the fridge and cut the roll into 1 inch slices.