Crowd pleasing mini Nanaimo bar bites

Ingredients

• 1/4 cup unsalted butter, cubed
• 2 tablespoons packed dark brown sugar
• 3 tablespoons cocoa powder
• 1 teaspoon vanilla bean paste or vanilla extract
• 1/2 teaspoon kosher salt
• 1 large egg, lightly beaten
• 3/4 cups almond flour
• 1/2 cup unsweetened shredded coconut, toasted
• 1/4 cup walnuts, toasted and finely chopped
• 1/2 cup unsalted butter, softened
• 2 tablespoons custard powder
• 1/4 cup whipping cream
• 2 cups icing sugar
• 1 1/2 cups dark chocolate, chopped
• 5 tablespoons unsalted butter
• Flaky sea salt, for garnish