Preheat your oven to 375°F (190°C). Brush the wells of a 12-cup standard muffin tin with the melted butter. This helps prevent sticking and adds flavor to the crusts.

Unroll the refrigerated pie crusts onto a lightly floured surface. Using a 3.5 to 4-inch round cookie cutter or the rim of a glass, cut out 12 circles from the pie crusts. You may need to re-roll scraps to get all 12 circles.

Carefully press each pie crust circle into the prepared muffin tin wells, gently shaping them to fit the bottom and sides.

In a large mixing bowl, whisk together the large eggs, heavy cream (or whole milk), salt, black pepper, and optional cayenne pepper until well combined and slightly frothy.

Stir in the shredded sharp cheddar cheese and Monterey Jack cheese until evenly distributed in the egg mixture.

Carefully pour the egg and cheese mixture into each pie crust-lined muffin well, filling them about three-quarters full.

Bake in the preheated oven for 25-30 minutes, or until the egg tarts are puffed, set in the center, and golden brown around the edges. A knife inserted into the center should come out clean.

Once baked, remove the muffin tin from the oven and let the tarts cool in the tin for 5-10 minutes before carefully removing them. This helps them firm up and prevents breaking.

Garnish with fresh chopped chives, if desired, and serve warm or at room temperature.