In a medium saute pan add the butter and saute the onion over medium heat for about 4 min. Add the garlic and saute for another 1-2 min. Stir in the flour and cook stirring for 1 min. Whisk in the stock and milk slowly. Add in the salt, pepper and paprika. Continue to whisk until mixture bubbles and thickens. Remove from heat and set aside.
Have all ingredients prepared and then peel and slice the potatoes, into ⅛” slices. Place half of the potatoes in the bottom of the greased pan. Top with ½ the sauce and 1 cup of cheddar cheese. Repeat. Bake for 30-40 min. with the cover on or aluminnum foil. Then remove the lid or foil and bake for 30 min. or until bubbly, browned and the potatoes are tender.