It’s a salad? Looks like mash… yeah… either way.
But it’s not dressed with butter but mayonnaise, so I guess that makes it a salad.

I ate something similar at a local Japanese food joint, Tenka Noshoku
But it lacked that tackiness… I think it’s due to the type of potatoes used as mine is on the white side, and theirs is more yellow. My hubby finds that ‘tackiness’ to be a plus point.

I used Kewpie mayo for this salad, as Tenka Noshoku doesn’t use regular mayo even as dips, what more for this salad.

Potato Salad with Apple

Tasted and recreated from Tenka Noshoku 
Serves 4 to 6

4 floury potatoes of choice (800gm unpeeled weight)
1/3 cup Kewpie Japanese style mayonnaise (estimated, as I used roughly 1/4 of a 310gm bottle)
Salt and pepper to taste
1/2 tsp rice vinegar
1 Fuji apple

1. Peel potatoes and cut into half. Cook in a pot of boiling water (add 2/3 tsp salt to the water) until soft.
2. Lightly mash the potatoes and then let them cool down a bit.
3. Add mayonnaise and seasoning and mix around. Add more mayonnaise if you prefer, I’m keeping it slim.
4. Keep chilled until time to serve.
5. Dice the apples small and mix with the potatoes. Serve cold .

Version 2 (updated 9/12/2014, my kids prefer this )
600gm chat potatoes
4 Tbsp Kewpie Mayo
1 Tbsp butter
3 Tbsp milk
Salt and pepper to taste
1 Fuji apple

Instructions: Almost the same. Add butter and milk when you mash the potatoes.