As easy as it is to bake a mug cake, or microwave for that matter, the same baking fiascos apply to even a plain 2-minute brownie, even more so because it is in a mug with a lesser surface area. The most common areas of goofing up are overdoing the brownie batter and not getting the ratios of the ingredients right. Usually, all of the ingredients for mug desserts tend to use an equal amount of everything.
Use proper measuring spoons for flour, cocoa powder, milk, and oil, especially for a mug brownie. Do not use regular kitchen spoons; they're inaccurate and will not give you the best results. Too much flour will make the brownie dry and dense. Too much milk will make it soggy. Cocoa powder is strong, so even 1 extra spoonful can make it bitter. Stick to the recipe, which might stipulate adding 3 tablespoons each of flour, cocoa powder, oil, and milk. Make sure you level off each ingredient measured with a knife.
Oil keeps the brownie soft and moist, more than butter, and is perfect for a small batch like a mug brownie, for oil makes it lighter and helps it stay fresh for longer. Butter changes how the brownie bakes in the microwave and does better in oven-baked, larger batch brownies to give them a tender crumb and a richer flavor. Butter also tends to firm up as it cools, which can make the brownie feel stiff or dry after a few minutes. Use sunflower oil, vegetable oil, or canola oil. Avoid olive oil, no matter how healthy it is; it will give your mug brownie an odd flavour that will mask the taste of the chocolate and other ingredients.
First, mix the sugar with the liquid ingredients until it is completely dissolved. Then add the dry ingredients, sift if needed to get rid of lumps that are hard to dissolve, especially teeny tiny ones. Mix the batter just until all the dry flour and cocoa are combined; don’t keep stirring! If you go overboard and mix too much, you will activate the gluten in the flour, which will yield you a dense brownie with more chew than softness. On the other hand, if you mix too little, you’ll end up with dry clumps that don’t cook, which aren’t mixed well into the batter in the first place. Use a spoon or fork and stop mixing once you don’t see any dry patches in the mug. Lift the spoon or fork and watch the batter drip off to be sure.
Choose a ceramic mug that holds at least 1 cup (250ml) of liquid. If your mug is too small, the batter will overflow in the microwave. If it’s too wide, the brownie will cook unevenly. A standard-sized coffee mug works well. Avoid plastic mugs, which can melt or warp, check the label to avoid any mishaps.
Microwave time depends on wattage. If your microwave is 1000 to 1200 watts, cook for 1 minute. If it’s below 1000 watts, cook for 90 seconds to 2 minutes. Stop after the first minute and check. Stick a toothpick or spoon into the center. If it comes out with wet batter, cook for 10 seconds more. If it comes out with moist crumbs, it’s done. If it’s totally clean, you’ve overcooked it.
The brownie will still be soft and slightly underdone when the microwave stops. Let it sit on the counter for 5 minutes. During this time, it will continue cooking with residual heat. This helps the center set properly and improves the texture. If you eat it too soon, it might taste gooey or raw in the middle.
Even a tiny amount of salt improves the flavor. It reduces bitterness and brings out the chocolate. Use just a pinch, less than ⅛ teaspoon. Vanilla essence (½ teaspoon) rounds out the flavor. Without it, the brownie can taste flat. These ingredients don’t affect texture directly, but they make the overall eating experience better, and the taste feels more balanced.