In a microwave-safe mug, melt butter in microwave for 15-30 seconds.
Once butter is melted, swirl around in mug to coat the sides. Add all remaining ingredients. Stir to combine. Microwave 1 minute 15 seconds. If the top is still soft, microwave again in 15-second increments. Mine was done in about a minute and 45 seconds. It should be springy and easily come out of the mug when you run a dull knife around the edges. Remove from mug and slice in half. Serve with sliced strawberries and whipped cream.