Uniform estimates for a family of Poisson problems: `rounding up the corners'

We prove uniform solvability estimates for certain families of elliptic problems posed in a family of domains that converge to another domain. We provide uniform estimates both in weighted and in usual Sobolev spaces. When the limit domain is a polygon, our results amount to ``rounding up'' the corners of the limit domain. The technique of proof is based on a suitable conformal modification of the metric, which makes the union of the domains a manifold with boundary and relative bounded geometry.