• Brownies
• Position a rack in the center of the oven and preheat to 350°. Use the softened butter to butter 10 standard muffin tins.
• Place the butter in a small, heavy-bottomed saucepan set over the lowest possible heat. Add the chocolate chips and melt together, stirring frequently to prevent the chocolate from scorching. Continue cooking until the mixture is pleasantly warm, but not too hot, to the touch. Remove from the heat and keep warm.
• Sift the flour into a small bowl to remove any lumps and set aside.
• Meanwhile, place the eggs, sugar and salt in the bowl of a stand mixer fitted with the paddle attachment and whip on medium-high speed until the mixture is very light and fluffy, 5 minutes.
• Turn the mixer to low and stir in the vanilla until just combined, then the warm chocolate-butter mixture. Add the flour and mix on low until combined. Remove the bowl from the mixer and use a flexible silicone spatula to give the batter a final stir by hand, scraping the bottom of the bowl and making sure all the flour is incorporated.
• Scrape the batter into the prepared muffin tins and smooth into an even layer. Bake the brownies until the top is puffed and a toothpick inserted into the center comes out with moist crumbs, 15-25 minutes, taking care not to overbake.
• Remove the brownies from the oven and flatten the tops with the back of a spoon; this will make them easier to decorate. Let the brownies cool slightly, then remove from the muffin tins to cool completely.
• The brownies keep well, airtight at room temperature, for up to 3 days, or refrigerated for up to 5 days.

Ganache Topping

• Place the bittersweet or semi-sweet chocolate chips in a medium bowl.
• In a small saucepan, heat the cream to a bare simmer. Pour the hot cream over the chocolate. Let sit for 1 minute, then whisk until smooth. Let cool to a spreadable consistency.
• Place the white chocolate chips in a small, heatproof bowl and set over a pan of barely steaming (not simmering water. Remove the pan from the heat and stir the white chocolate frequently until melted and smooth. Take care not to overheat the white chocolate or contaminate with any moisture or it will seize up.
• Scrape the white chocolate into a cone made from parchment paper and cut a tiny hole in the bottom. Alternatively use a small piping bag fitted with a very small plain tip. Keep warm.
• Spread one brownie with the soft ganache. Immediately pipe the white chocolate in a tight spiral over the top. Right away, drag a toothpick through the white chocolate and ganache, starting in the center and pulling outwards. Repeat this 6-8 times around the brownie to make a spiderweb pattern.
• Repeat with the remaining brownies.
• The cakes can be stored up to 1 day at room temperature.