1. Combine butter, brown sugar, vanilla, salt and egg in a bowl and whisk until smooth. Add flour, oats and chocolate chips and stir until all ingredients are moistened and well combined.
2. Divide dough among six large microwave-safe mugs or ramekins (using about 1/3 cup batter for each). Microwave on high power, one at a time, until cookies are just baked around edges but still soft in center, 45 seconds to 1 minute. Serve immediately.