Preheat the oven to 400 degrees.
Melt the butter in a small skillet or saucepan over medium heat.
Place the cream cheese, heavy whipping cream, dijon and salt and pepper to taste into a food processor or blender, and pulse until smooth.
Add the cream sauce to the skillet with the butter, and whisk until smooth and thickened.
Remove the sauce and let cool.
Line a large baking sheet with parchment paper or a silicone baking mat.
Arrange the cheese into 6 small circles on the baking sheet, leaving some room between each circle.
Bake for 6-8 minutes until the cheese takes on a lace-like appearance, and the edges start to brown and crisp up.
While the cheese is baking, combine the tuna fish, celery, red onion, parmesan and cream sauce in a bowl until well blended. Add salt and pepper to taste.
Remove the cheese from the oven, and let cool for a few minutes.
While the cheese circles are still pliable, add a layer of the tuna fish filling down the center of each one.