Black Hole Cosmology has traditionally been challenged by the apparent incompatibility between black hole interiors and cosmic expansion. However, because classical general relativity, on which this criticism is based, is itself incomplete in black hole interiors, the criticism rests on an incomplete premise. We reformulate this problem using total gravitational self-energy (GSE). The total GSE functional U_{gs−T}(R) = − (βGM_fr^2/R)[1 − (5β/7 )GM_fr/ Rc^2] contains a negative GSE term and a positive matter-GSE interaction term responsible for the repulsive radial response, where β denotes the structural coefficient of the GSE functional. For a matter-filled black hole interior, this energy landscape yields finite radii, including R_gs=(5β/7)R_S, R_{min,BH} = 5βR_S/(14−5β), and R_{min,E}=(5β/14)R_S. Thus, the point singularity is replaced by a finite-radius structure, allowing sufficiently massive black holes to contain macroscopic nonsingular interiors. This supports the possibility of closed black hole universes whose interiors exhibit weak local curvature and small tidal gradients. For our observable universe, the relevant configuration is not an isolated vacuum black hole, but a cosmological black hole embedded in a much larger, nearly homogeneous matter distribution. The matter-sector mass enclosed within the present particle horizon gives a Schwarzschild-equivalent event horizon radius R_S≃150.4 Gly, whereas the causal radius is R_U≃46.5Gly, giving R_S/R_U≃3.23 > 1. In this compactness sense, the observable universe lies within its own Schwarzschild-equivalent radius. The cosmological application of total GSE yields the dark energy density ρ_{Λ_m}= (βρ_m/2)(R_S/R_U)[(5β/14)R_S/R_U − 1]. Under the matter-dominated background approximation with w_{Λ_m}≃−1, the condition for accelerated expansion is ρ_{Λ_m} > ρ_m/2, or equivalently, R_U< R_{crit,U}≃0.279 βR_S. The framework provides a three-stage interpretation of cosmic history: early accelerated expansion driven by total GSE, a decelerating phase during the radiation era and the matter era, and late-time accelerated expansion driven by total GSE dark energy. Thus, accelerated cosmic expansion is not evidence against Black Hole Cosmology, but rather a central signature of a cosmological black hole. The predicted dark energy density provides a direct observational test of this interpretation of the observable universe.