Profiteroles with Coffee Ice Cream

Chill a small metal baking pan in freezer. Form 18 ice cream balls with scoop and freeze in chilled pan at least 1 hour (this will make serving faster).
Preheat oven to 425°F with rack in middle. Butter a large baking sheet.
Bring butter, water, and salt to a boil in a small heavy saucepan, stirring until butter is melted. Reduce heat to medium, then add flour all at once and cook, beating with a wooden spoon, until mixture pulls away from side of pan and forms a ball, about 30 seconds. Transfer mixture to a bowl and cool slightly, 2 to 3 minutes.
Add eggs 1 at a time, beating well with an electric mixer after each addition.
Transfer warm mixture to pastry bag and pipe 18 mounds (about 1 1/4 inches wide and 1 inch high) 1 inch apart on baking sheet.
Bake until puffed and golden brown, 20 to 25 minutes total. Prick each profiterole once with a skewer, then return to oven to dry, propping oven door slightly ajar, 3 minutes. Cool on sheet on a rack.
Heat sugar in a 2-quart heavy saucepan over medium heat, stirring with a fork to heat sugar evenly, until it starts to melt, then stop stirring and cook, swirling pan occasionally so sugar melts evenly, until it is dark amber.
Remove from heat, then add cream and a pinch of salt (mixture will bubble and steam). Return to heat and cook, stirring, until caramel has dissolved.
Remove from heat and add chocolate, whisking until melted, then whisk in vanilla and Cognac (if using). Keep warm, covered.
Halve profiteroles horizontally, then fill each with a ball of ice cream. Put 3 profiteroles on each plate and drizzle generously with warm chocolate sauce.