Mix in 2 tablespoons milk, 1 egg and 1/8 teaspoon salt. Add 2 tablespoons coconut flour and 1/2 teaspoon baking powder and mix until thoroughly combined.
Microwave the batter for 90 seconds. Allow to rest for a minute, then carefully run a knife around the edges and release the bread from the container. If the bottom sticks, carefully run a small spatula underneath. Place the bread on a wire rack and allow to cool while you make another slice.
Repeat steps 1-3 to make a second slice of keto bread.
Heat 1 tablespoon butter in a nonstick skillet over medium-low heat. Assemble the sandwich: place 2 cheese slices between the keto bread slices you just made.
When butter foams, place the sandwich in the skillet. Cook until bread is golden brown and cheese is melted, 3-5 minutes per side over medium-low heat. Press on the sandwich with a large spatula, or better yet, place a heavy pot on it, as shown in the video.
Transfer the keto grilled cheese sandwich to a cutting board. Cut into two triangles and serve.