In an Instant Pot add potatoes, garlic, water, salt and one and a half tablespoons butter. Put the lid on, turn the valve to sealing and cook on manual high pressure for 8 minutes. (My Instant Pot took 10 minutes to come to pressure, so the total time taken was 18 minutes). Release pressure immediately by turning the knob to 'vent', and open the lid once the pressure is released.

Using a potato masher, mash the potatoes in the Instant Pot for really creamy potatoes. For fluffier mashed potatoes, you can drain the water and then mash the potatoes. Once the potatoes are mashed, mix in the remaining butter, sour cream and cream cheese. Mix well while the potatoes are still steaming hot. Taste and add more salt if required. Top with more butter and chives and serve.