Sauté onions in butter over medium high heat until onions are translucent. About 5 minutes.

Slowly add flour, stirring continuously. Trying for an almost paste like consistency.

Slowly add chicken stock, stirring continuously.

Slowly add milk, again stirring continuously.

Once milk is added, heat until soup starts to thicken. Stir occasionally to make sure nothing is sticking to the bottom of the pan. (about 10 minutes)

While soup is thickening, cook cubed chicken until no pink shows. Add sliced kielbasa and cook until it starts to brown.

Slowly add cubed Velveeta to soup. Add a little, stir, add a little more, stir again.

After Velveeta is added and has fully melted, add chicken and kielbasa.

Stir everything well to combine