In a medium bowl, crumble 16 ounces of feta cheese and add 5 ounces of grated kefalograviera. Sprinkle with freshly cracked pepper to taste. Gently mix until well combined.

On a clean and dry surface, lay out one sheet of defrosted phyllo dough. Brush lightly with olive oil. Sprinkle a portion of the cheese mixture over the phyllo, covering it evenly. Repeat with two more phyllo sheets, brushing with oil and adding cheese each time.

Starting from the long side, gently roll the phyllo sheets into a tight log, tucking the ends inward to secure the filling.

Wrap the rolled log tightly in plastic wrap and place it in the freezer for at least one hour or longer.

Preheat your oven to 350°F (175°C). Let the frozen log sit at room temperature for about 10 minutes. Cut into 1-inch slices and arrange on a greased baking pan. Bake for 20 to 30 minutes, or until golden brown.

Once out of the oven, let the bites cool for a few minutes. Serve warm with tzatziki or enjoy as is.