Combine the almond flour, tapioca flour, salt, Parmesan cheese and butter in a food processor, or use a pastry blender in a bowl. Pulse or blend until the texture of coarse meal.
Add 1 egg and pulse/mix again until dough comes together. Turn out the dough onto a piece of plastic wrap, shape it into a flat round disk, and refrigerate for at least 1 hour or up to 3 days.
When ready to bake, slice the heirloom tomatoes into medium-thick slices. Lightly salt the tomato slices - this will help draw out a bit of extra moisture. Slice the mozzarella cheese into thin slices.
Lightly press both the tomatoes and mozzarella slices between two paper towels to help get rid of any extra moisture and pat them dry.
When you're ready to bake, preheat your oven to 375°F.
Remove the dough from the refrigerator and roll the dough out between two pieces of parchment paper into a large circle. You want it thick enough to be able to hold the filling and fold up the sides.
Arrange the heirloom tomatoes and mozzarella as desired - I arranged them in a circular pattern, alternating slices of each. Place the roasted garlic cloves among the tomatoes and mozzarella. Sprinkle salt and pepper on top, to taste.
Gently fold the sides up, creasing the dough together with your fingers as you go. I used the parchment to help fold up the dough so it didn’t break.
Beat the remaining egg with a splash of water in a small bowl. Brush the outside edges of the galette with the egg wash. Sprinkle the crust with a little more Parmesan cheese.
Transfer the parchment with the galette to the baking sheet and bake for 30-35 minutes until the edges are golden brown and the cheese is bubbly. Check at 25 minutes and tent with foil if it’s browning too quickly.
Remove from the oven and garnishing with fresh basil before slicing and serving.