Preheat the oven to 425°F.

Spray 5 custard cups with baking spray and place on a baking sheet.

Microwave the butter and chocolate in a large bowl on high until the butter is melted, about 1 minute. Whisk until the chocolate is also melted.

Stir in the sugar until well blended. Whisk in the eggs then add the vanilla. Stir in the flour.

Divide the mixture among the custard cups.

Bake until the sides are firm and the centers are soft, about 10-12 minutes. Let stand 2 minute.

Invert on individual plates while warm and serve with vanilla ice cream.