In a medium saucepan, combine parsnips and potato. Add enough water to cover and cook for 20 minutes. Drain in a colander.
In two batches, puree half the parsnip-potato mixture, half the pear, 1/2 teaspoon salt, 1 tablespoon butter, and half the heavy cream in a food processor, pulsing until smooth. Repeat process and combine both batches in saucepan. Stir in remaining 1/2 teaspoon salt and Cognac. Serve warm.